Nanometer to Mil/Thou Converter
Convert nanometers to mils with our free online length converter.
Quick Answer
1 Nanometer = 0.0000394 mils
Formula: Nanometer × conversion factor = Mil/Thou
Use the calculator below for instant, accurate conversions.
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All conversion formulas on UnitsConverter.io have been verified against NIST (National Institute of Standards and Technology) guidelines and international SI standards. Our calculations are accurate to 10 decimal places for standard conversions and use arbitrary precision arithmetic for astronomical units.
Nanometer to Mil/Thou Calculator
How to Use the Nanometer to Mil/Thou Calculator:
- Enter the value you want to convert in the 'From' field (Nanometer).
- The converted value in Mil/Thou will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Length category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Nanometer to Mil/Thou: Step-by-Step Guide
Converting Nanometer to Mil/Thou involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Nanometer = 3.9370e-5 milsExample Calculation:
Convert 10 nanometers: 10 × 3.9370e-5 = 0.000393701 mils
Disclaimer: For Reference Only
These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.
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View all Length conversions →What is a Nanometer and a Mil/Thou?
A nanometer (symbol: nm) is a unit of length in the International System of Units (SI) equal to one billionth (10⁻⁹) of a meter:
1 nm = 0.000000001 m = 1 × 10⁻⁹ m
Why Is the Nanometer Scale Special?
The nanometer occupies a unique position between the atomic world and the microscopic world visible under optical microscopes:
1. Atomic to Molecular Scale:
- Individual atoms: 0.1-0.3 nm diameter (hydrogen to larger elements)
- Small molecules: 0.3-2 nm (water, glucose, amino acids)
- Large biomolecules: 2-100 nm (proteins, DNA, ribosomes)
2. Quantum Effects Dominate:
- At nanometer scales, quantum mechanical effects become significant
- Electrons exhibit wave-particle duality
- Quantum tunneling allows particles to pass through barriers
- Energy levels become quantized (discrete rather than continuous)
- Materials exhibit size-dependent properties (quantum dots change color with size)
3. Surface Area to Volume Ratio:
- Nanoparticles have enormous surface area relative to volume
- This makes them extremely reactive and useful for catalysis
- Example: Gold is chemically inert in bulk but highly reactive as 5nm nanoparticles
4. Optical Properties Change:
- Materials interact differently with light at nanometer scales
- Nanostructures can manipulate light in ways impossible with bulk materials
- Metamaterials with negative refractive index
- Plasmonic effects in metal nanoparticles
The Nanometer in Context
Too Small to See with Optical Microscopes:
- Optical microscopes use visible light (wavelengths 400-700nm)
- Diffraction limit: Cannot resolve features smaller than ~200nm (half the wavelength)
- Viewing nanometer-scale structures requires:
- Electron microscopes (transmission or scanning, resolution to 0.1nm)
- Scanning probe microscopes (STM, AFM, can "feel" individual atoms)
- X-ray crystallography (infers structure from diffraction patterns)
Larger Than Individual Atoms:
- Atoms: 0.1-0.3nm diameter
- Nanometer scale: 1-100nm (roughly 3-300 atoms wide)
- This is the realm of molecules, nanoparticles, viruses, and proteins
What is a Mil?
A mil (also called thou) is a unit of length in the imperial measurement system equal to one thousandth of an inch. The mathematical definition is:
1 mil = 0.001 inch = 1/1000 inch = 25.4 micrometers (μm) = 0.0254 millimeters
The mil is not a metric unit and should not be confused with the millimeter (mm), despite similar-sounding names. This confusion is one of the most common measurement errors in international manufacturing:
- 1 mil (imperial) = 0.0254 mm = 25.4 μm
- 1 millimeter (metric) = 39.37 mils = 1,000 μm
The mil exists as a natural subdivision of the inch, providing a convenient decimal-based measurement for very small imperial dimensions without resorting to awkward fractions like 1/1000″.
Mil vs. Thou: Regional Terminology
The terms "mil" and "thou" are completely interchangeable and refer to the exact same measurement:
- Mil: Predominant in American English, technical documentation, industry standards (ASTM, ANSI), and scientific contexts. The name derives from Latin "mille" (thousand).
- Thou: Common in British English shop-floor terminology, machining, and colloquial engineering speech. It's an abbreviated form of "thousandth" (of an inch).
Example usage:
- American engineer: "The coating should be 5 mils thick."
- British machinist: "Machine this to within 2 thou tolerance."
- Both mean the same thing: 0.005″ and 0.002″ respectively.
Decimal Imperial vs. Fractional Imperial
The mil represents a decimal approach to imperial measurement, contrasting with the traditional fractional approach:
Fractional imperial (traditional):
- 1/2″, 1/4″, 1/8″, 1/16″, 1/32″, 1/64″
- Awkward for very small measurements
- Difficult to add/subtract without common denominators
Decimal imperial (mils/thousandths):
- 0.500″ (500 mils), 0.250″ (250 mils), 0.125″ (125 mils)
- Easy arithmetic: 5 mils + 3 mils = 8 mils
- Natural compatibility with digital calipers and micrometers
Engineering drawings often show both: 0.250″ (1/4″) for clarity, but critical tolerances are always specified in decimal thousandths: ±0.005″ (±5 mils), never ±1/200″.
Mils in Wire Gauge Systems
American Wire Gauge (AWG) uses diameter in mils as the basis for its numbering system, though the relationship is logarithmic rather than linear:
| AWG Size | Diameter (mils) | Diameter (mm) | Common Use | |----------|----------------|---------------|------------| | 0000 (4/0) | 460 mil | 11.7 mm | Heavy power cables | | 00 (2/0) | 365 mil | 9.3 mm | Welding cable | | 10 AWG | 102 mil | 2.6 mm | Household 30A circuits | | 14 AWG | 64 mil | 1.6 mm | Household 15A circuits | | 18 AWG | 40 mil | 1.0 mm | Lamp cords, doorbells | | 22 AWG | 25 mil | 0.64 mm | Solid hookup wire | | 30 AWG | 10 mil | 0.25 mm | Wire-wrap wire | | 40 AWG | 3 mil | 0.08 mm | Magnet wire (coils) |
The AWG system was established in the 1850s based on the number of times wire was drawn through reducing dies, with each gauge step representing approximately a 20% reduction in diameter (factor of √2 for cross-sectional area).
Note: The Nanometer is part of the metric (SI) system, primarily used globally in science and trade. The Mil/Thou belongs to the imperial/US customary system.
History of the Nanometer and Mil/Thou
of the Nanometer and Nanotechnology
Early Foundations: Unknowingly Working at the Nanoscale (Pre-1900)
Ancient Nanomaterials (400 BCE - 1600 CE):
- Roman Lycurgus Cup (4th century CE): Contains gold-silver nanoparticles (~70nm) that make glass appear red in transmitted light, green in reflected light
- Medieval stained glass windows: Colloidal gold and other metal nanoparticles create vibrant colors
- Ancient artisans unknowingly created nanomaterials through empirical recipes
Michael Faraday's Colloidal Gold (1857):
- British scientist Michael Faraday systematically studied colloidal gold suspensions
- Discovered that gold nanoparticles (5-100nm) exhibit ruby-red color, unlike bulk gold's yellow
- First scientific recognition that material properties change at nanometer scale
- Published "Experimental Relations of Gold (and Other Metals) to Light"
- Laid foundation for nanoscience, though the term wouldn't exist for over a century
Theoretical Foundations (1900-1959)
Quantum Mechanics (1900-1930):
- Max Planck (1900): Quantum theory—energy is quantized
- Albert Einstein (1905): Photons (light quanta) and photoelectric effect
- Niels Bohr (1913): Atomic model with discrete electron orbits
- Erwin Schrödinger (1926): Wave equation describing electron behavior
- These developments revealed that matter behaves fundamentally differently at atomic/molecular scales
Electron Microscopy (1931):
- Ernst Ruska and Max Knoll invented the transmission electron microscope (TEM)
- First images of structures below optical resolution (sub-100nm)
- Enabled visualization of viruses, cell organelles, and eventually nanoparticles
The Birth of Nanotechnology Concept (1959-1980)
Richard Feynman's Vision (1959):
- Famous lecture "There's Plenty of Room at the Bottom" at Caltech
- Envisioned manipulating individual atoms to build materials and machines
- Predicted writing entire Encyclopedia Britannica on head of a pin
- Proposed molecular-scale machinery and atom-by-atom fabrication
- Didn't use term "nanotechnology" but inspired the field
Norio Taniguchi Coins "Nanotechnology" (1974):
- Japanese scientist Norio Taniguchi first used term "nanotechnology"
- Referred to precision machining and material processing with tolerances below 1 micrometer
- Initially described top-down manufacturing (machining, lithography)
- Later expanded to bottom-up assembly (molecular self-assembly)
The Nanotechnology Revolution (1981-Present)
Scanning Tunneling Microscope - STM (1981):
- Gerd Binnig and Heinrich Rohrer (IBM Zurich) invented STM
- First instrument to "see" and manipulate individual atoms
- Uses quantum tunneling effect to scan surfaces with atomic resolution
- Won Nobel Prize in Physics (1986)
- 1989: IBM scientists arranged 35 xenon atoms to spell "IBM" (first atomic-scale manipulation)
Atomic Force Microscope - AFM (1986):
- Gerd Binnig, Calvin Quate, and Christoph Gerber invented AFM
- Can image and manipulate atoms on insulators (not just conductors like STM)
- "Feels" surface topography with nanometer-scale probe
- Revolutionized nanoscale characterization across materials science, biology, chemistry
Fullerenes and Carbon Nanotubes (1985-1991):
- Harold Kroto, Robert Curl, Richard Smalley discovered buckminsterfullerene (C₆₀, 1985)
- Soccer-ball-shaped carbon molecule, ~0.7nm diameter
- Nobel Prize in Chemistry (1996)
- Sumio Iijima discovered carbon nanotubes (1991)
- Cylindrical carbon structures, 1-100nm diameter, micrometers long
- Exceptional strength, electrical conductivity, thermal properties
- Sparked explosion of nanomaterials research
Semiconductor Nanometer Process Nodes (1990s-Present):
Moore's Law and the Nanometer Era:
- Gordon Moore (1965): Predicted transistor count per chip would double every ~2 years
- Drove relentless miniaturization of semiconductor features
Process Node Timeline:
- 130 nm (2001): Intel Pentium 4, first widespread "nanometer node"
- 90 nm (2004): AMD Athlon 64, Intel Pentium 4 Prescott
- 65 nm (2006): Intel Core 2 Duo, beginning of multi-core era
- 45 nm (2007): Intel Core 2 Duo (Penryn), high-k metal gates introduced
- 32 nm (2010): Intel Core i3/i5/i7 (Westmere)
- 22 nm (2012): Intel Ivy Bridge, first 3D FinFET transistors (non-planar)
- 14 nm (2014): Intel Broadwell, Apple A8
- 10 nm (2017): Intel Cannon Lake (limited), Samsung/TSMC volume production
- 7 nm (2019): AMD Ryzen 3000, Apple A12, extreme ultraviolet (EUV) lithography
- 5 nm (2020): Apple M1, AMD Ryzen 5000 (TSMC), advanced EUV
- 3 nm (2022): Apple M2 Pro/Max (late 2022), Apple A17 (2023)
- 2 nm (Development): Expected mid-2020s, pushing physical limits
Note: Modern "process nodes" (7nm, 5nm, 3nm) are marketing terms more than actual physical dimensions. A "5nm" chip doesn't necessarily have 5nm transistors; the smallest features may be 20-30nm. The naming reflects relative density improvements.
Contemporary Nanotechnology (2000-Present)
Nanomedicine:
- Nanoparticle drug delivery: Liposomes, polymeric nanoparticles target tumors
- mRNA vaccines (Pfizer-BioNTech, Moderna COVID-19 vaccines): Use lipid nanoparticles (~100nm) to deliver mRNA
- Gold nanoparticles for cancer therapy, diagnostics
- Quantum dots for biological imaging
Nanomaterials:
- Graphene (2004 isolation by Andre Geim and Konstantin Novoselov): Single-atom-thick carbon sheet, extraordinary properties
- Quantum dots: Semiconductor nanocrystals (2-10nm) that emit specific colors based on size
- Aerogels: Ultra-low-density nanoporous materials
Consumer Applications:
- Sunscreen: Titanium dioxide and zinc oxide nanoparticles (transparent, UV-blocking)
- Anti-reflective coatings: Nanoporous silica on eyeglasses, displays
- Stain-resistant fabrics: Nanoparticle coatings
- Catalytic converters: Platinum nanoparticles
Ancient and Medieval Precision (Before 1700)
Before the Industrial Revolution, precision measurement was limited by available tools. Ancient civilizations measured small lengths using:
- Barleycorns: 1 inch = 3 barleycorns (still referenced in shoe sizing)
- Hair breadth: Approximately 1/48 of an inch (about 21 mils)
- Poppy seed: Medieval unit ≈ 1/72 inch (14 mils)
These natural standards were inconsistent but adequate for carpentry, masonry, and traditional crafts where tolerances of 1/16″ to 1/32″ were acceptable. Precision metalworking (locksmithing, clockmaking, weapon-smithing) relied on master craftsmen's skill and direct comparison to reference standards rather than numerical measurement.
The finest medieval measurements were in clock and instrument making, where tolerances approaching 1/100″ (10 mils) were occasionally achieved, but not reliably measured or documented.
Industrial Revolution and the Birth of Precision (1750-1850)
The transformation of manufacturing from craft to industry created an urgent need for precision measurement:
1775-1800: John Wilkinson's cylinder boring machine (1775) achieved tolerances within 1/20″ (50 mils) for steam engine cylinders—revolutionary at the time, enabling James Watt's efficient steam engines.
1800-1840: Interchangeable parts manufacturing emerged. Eli Whitney's 1798 contract to produce 10,000 muskets with interchangeable parts required consistent tolerances around 1/32″ (31 mils), though he struggled to achieve this consistently.
1840s: Joseph Whitworth revolutionized precision measurement:
- Invented the first practical micrometer (1840s), capable of measuring to 0.001″ (1 mil)
- Developed precision surface plates and scrapers
- Standardized screw threads with tolerances of a few thousandths
- Established the "thou" as the standard British precision unit
Whitworth's work meant that for the first time, machinists could reliably measure and verify work to within one thousandth of an inch, making the mil/thou a practical working unit rather than a theoretical ideal.
1850s: American System of Manufacturing (Colt, Robbins & Lawrence, Singer) adopted decimal measurements in thousandths for gauging and inspection, establishing "mils" in American technical vocabulary.
Standardization and Proliferation (1850-1920)
1860s-1880s: Development of precision measuring instruments:
- Vernier calipers graduated in thousandths
- Micrometer calipers (marketed by Brown & Sharpe from 1867)
- Dial indicators (from 1890s) showing 0.001″ divisions
1857: American Wire Gauge (AWG) standardized by J. R. Brown, using wire diameter in mils as the basis.
1880s-1900s: Paint and coating industries adopted mils for dry film thickness:
- Paint manufacturers specified coverage rates based on mils of dry film
- Wet film thickness gauges calibrated in mils
- Quality standards (e.g., U.S. Navy specifications) required minimum coating thickness in mils
1900-1920: Sheet metal gauges proliferated (ironically, these use arbitrary numbering systems, but actual thickness is specified in decimal inches/mils):
- Manufacturer's Standard Gauge (MSG) for steel
- Birmingham Wire Gauge (BWG)
- Confusion from multiple gauge systems led to increasing use of direct mil specifications
1916: SAE (Society of Automotive Engineers) founded, establishing thousands of specifications with tolerances in thousandths of an inch for automotive parts.
Electronics Age and Micro-Precision (1920-1980)
1930s-1940s: Electronics manufacturing adopted mils for:
- Wire insulation thickness (enamel on magnet wire: 0.5-2 mils)
- Capacitor dielectric thickness
- Vacuum tube electrode spacing
1943: Printed Circuit Board (PCB) invention (Paul Eisler, 1943; mass production 1950s):
- Copper foil thickness: 1.4 mils (1 oz/ft²), 2.8 mils (2 oz/ft²)
- Trace width: typically 5-15 mils for signal traces
- Spacing between traces: 5-8 mils minimum in early designs
- PCB substrate thickness: 62 mils (1.57 mm) became standard
1950s-1960s: Plastic film industry standardized thickness in mils:
- Polyethylene film (bags, wrap): 0.5-6 mils
- Polyester film (Mylar): 0.5-10 mils
- Vinyl flooring underlayment: 6-20 mils
1960s: Integrated circuit (IC) manufacturing pushed precision far beyond mils:
- Early transistors: features measured in tens of mils
- By 1970: features approaching 100 microinches (0.1 mil)
- The mil remained relevant for IC package dimensions, lead spacing, and encapsulation thickness
1975: ANSI/ASTM standards codified mil-based specifications for coating thickness, plastic film, and adhesive tape across dozens of industries.
Modern Era and Metrication Resistance (1980-Present)
1980s-1990s: Global metrication movement:
- Britain officially metricated in 1965-1995, but "thou" persisted in machine shops
- U.S. industries largely resisted metrication in favor of established decimal-inch (mil) systems
- Aerospace, defense, and automotive industries retained imperial specs due to:
- Enormous legacy of existing designs, tooling, and parts libraries
- Cost of converting decades of technical documentation
- Risk of conversion errors (Mars Climate Orbiter lost in 1999 due to metric/imperial confusion)
1990s-2000s: PCB design and microelectronics:
- PCB CAD software (OrCAD, Altium, Eagle) defaulted to mil grid spacing (5 mil, 10 mil, 25 mil grids)
- Modern PCB fabrication: 3-4 mil traces/spaces achievable in standard processes
- Advanced processes: sub-mil features (0.5 mil), but package and board dimensions still in mils
2000s-Present: Hybrid metric/imperial usage:
- American manufacturing: Part dimensions often in inches/mils, tolerances in mils
- International suppliers: Provide both metric and mil equivalents
- 3D printing: Software often accepts both (mil settings for layer height, nozzle diameter)
- Coating industry: Paint thickness gauges typically show both mils and microns
Present day: The mil remains dominant in:
- American PCB and electronics manufacturing
- U.S. aerospace and defense (military specifications)
- Coating and painting (ASTM standards)
- Plastic film and flexible packaging
- American Wire Gauge system
- Machining tolerances in U.S. shops
Common Uses and Applications: nanometers vs mils
Explore the typical applications for both Nanometer (metric) and Mil/Thou (imperial/US) to understand their common contexts.
Common Uses for nanometers
of the Nanometer in Modern Contexts
1. Technology and Electronics
Semiconductors:
- Process node naming (3nm, 5nm, 7nm chips)
- Transistor gate lengths, interconnect widths
- Thin film thicknesses (oxides, metals, dielectrics)
Displays:
- QLED quantum dots (2-10 nm) for color purity
- OLED organic layers (~100 nm thick)
- Anti-reflective coatings (100-150 nm)
Data Storage:
- Hard drive head-to-platter spacing (~3-5 nm flying height)
- Magnetic domain sizes (~10-50 nm)
- Flash memory cell feature sizes (~15-30 nm)
2. Optics and Photonics
Wavelength Specifications:
- Laser wavelengths (UV: 193 nm, 248 nm, 355 nm; visible: 405 nm, 532 nm, 650 nm)
- Optical filter bandwidths (specify transmission/reflection in nm ranges)
- Spectroscopy (absorption/emission peaks reported in nanometers)
Thin Film Optics:
- Anti-reflective coatings (multiple layers, each 50-150 nm)
- Dichroic mirrors and filters (nanometer-scale multilayers)
- Photonic crystals (periodic structures, 100-500 nm)
3. Materials Science and Nanotechnology
Nanoparticle Synthesis:
- Specifying target particle size (gold nanoparticles: 5, 10, 20, 50, 100 nm)
- Quantum dots (size determines optical properties)
- Ceramic nanoparticles for catalysis, coatings
Thin Films and Coatings:
- Physical vapor deposition (PVD), chemical vapor deposition (CVD)
- Layer thicknesses: 1-1,000 nm
- Atomic layer deposition (ALD): atomic-scale control (~0.1 nm/cycle)
Surface Characterization:
- Atomic force microscopy (AFM) measures roughness in nanometers
- Ellipsometry measures film thickness (0.1-1,000 nm range)
- Scanning electron microscopy (SEM) images nanoscale features
4. Biology and Medicine
Molecular Dimensions:
- Protein sizes (5-50 nm typical)
- Virus dimensions (20-400 nm)
- Cell membrane thickness (~7-10 nm lipid bilayer)
Nanomedicine:
- Nanoparticle drug carriers (50-200 nm optimal for cellular uptake)
- mRNA vaccine lipid nanoparticles (~100 nm)
- Diagnostic nanoparticles (gold, quantum dots, magnetic)
Microscopy:
- Electron microscopy resolution (TEM: 0.1-1 nm, SEM: 1-10 nm)
- Super-resolution optical microscopy (breaks diffraction limit, ~20-50 nm resolution)
5. Environmental Science
Air Quality:
- Ultrafine particles: < 100 nm diameter (penetrate deep into lungs)
- PM 2.5: Particulate matter < 2,500 nm (2.5 μm) diameter
- Nanoparticle pollutants from combustion, industrial processes
Water Filtration:
- Nanofiltration membranes: pore sizes 1-10 nm (remove ions, small molecules)
- Graphene oxide membranes: sub-nanometer channels for desalination
6. Metrology and Precision Measurement
Surface Roughness:
- Optical surfaces: Roughness < 1 nm RMS (root mean square) for high quality
- Semiconductor wafers: < 0.1 nm RMS for epitaxial growth
Film Thickness:
- Quality control in manufacturing (coatings, semiconductors)
- Techniques: Ellipsometry, X-ray reflectivity, profilometry
7. Research and Development
Nanoscience Research:
- Synthesizing new nanomaterials with specific dimensions
- Characterizing structure-property relationships
- Exploring quantum effects at nanoscale
Academic Publications:
- Specifying material dimensions (nanoparticle size, film thickness, feature size)
- Nanometer is standard unit in materials science, nanotechnology, condensed matter physics
When to Use mils
1. Precision Manufacturing and Machining
The mil is the fundamental tolerance unit in American manufacturing:
Engineering drawings and blueprints:
- Nominal dimensions in decimal inches: 1.250″, 0.375″
- Tolerances in thousandths: ±0.005″ (±5 mils), ±0.002″ (±2 mils)
- Geometric dimensioning and tolerancing (GD&T): Position tolerance ⌖ 0.010″ (10 mils)
Quality control and inspection:
- Calipers and micrometers graduated in 0.001″ (1 mil) divisions
- Dial indicators show 0.001″ or 0.0001″ (0.1 mil) graduations
- Coordinate measuring machines (CMM) measure to ±0.1 mil or better
- Pass/fail gauges: "Go" and "No-Go" plugs/rings differ by a few mils
Real-world tolerances by industry:
- General fabrication: ±5-10 mils (±0.005-0.010″)
- Automotive production: ±2-5 mils typical
- Aerospace critical parts: ±0.5-2 mils
- Medical implants (hip, knee): ±0.2-1 mil
- Semiconductor equipment: ±0.1 mil (±100 microinches)
Example: A shaft specified as Ø 1.000″ ± 0.002″ must measure between 0.998″ and 1.002″ (within ±2 mils). A shaft measuring 1.003″ (3 mils over) would be rejected.
2. Coating Thickness Measurement
Paint, plating, and protective coating thickness is universally measured in mils in American industry:
Paint inspection (wet film thickness gauges):
- Notch gauges (comb-style): Teeth graduated in mils (2, 4, 6, 8, 10 mils)
- Painter inserts gauge into wet paint; highest clean tooth indicates thickness
- Ensures proper coverage to meet specification (e.g., "apply to 6 mils wet film")
Dry film thickness (DFT) measurement:
- Magnetic gauges (ferrous substrates): Reed sensor or Hall effect, calibrated in mils
- Eddy current gauges (non-ferrous): For aluminum, brass, copper substrates
- Ultrasonic gauges: For non-metallic coatings on any substrate
Industry specifications:
- SSPC-PA 2 (paint inspection): Requires DFT measurement in mils
- U.S. Navy painting specs: Minimum DFT requirements (e.g., 5-7 mils for topcoat)
- Automotive OEM specs: Total paint system 4-6 mils
- Industrial maintenance coatings: Often 8-15 mils for severe environments
Example: A steel bridge specification might require: "Apply epoxy primer to 5-8 mils DFT, followed by polyurethane topcoat to 3-5 mils DFT." Inspectors measure at multiple points; any reading below minimum triggers rework.
Galvanizing and plating:
- Hot-dip galvanizing: ASTM A123 requires minimum 2.0 mils (for <1/4″ thick steel)
- Chrome plating: 0.5-1 mil decorative, 8-10 mils hard chrome (wear resistance)
- Anodizing (aluminum): Type II = 0.2-0.7 mils, Type III (hard anodize) = 2-4 mils
3. Plastic Film and Flexible Packaging
Plastic film thickness is specified in mils in the U.S. packaging industry:
Food packaging films:
- Shrink wrap: 2-4 mils (60-100 μm)
- Stretch wrap (pallet wrap): 12-20 gauge = 0.5-0.8 mil (gauge ≠ mils, confusingly)
- Vacuum seal bags (FoodSaver): 3-4 mils
- Frozen food bags: 2-3 mils
- Thicker film = better puncture resistance, higher material cost
Construction and industrial films:
- Vapor barriers (under-slab): 6-10 mils required by building codes
- Construction tarps: 5-12 mils depending on duty
- Agricultural greenhouse film: 4-6 mils (UV-stabilized)
- Geomembrane liners (landfills, ponds): 20-100 mils
Adhesive tapes:
- Scotch tape (Transparent): 1-1.5 mils
- Masking tape: 5-7 mils total thickness
- Duct tape: 10-12 mils
- Double-sided foam tape: 30-60 mils
- Specification includes backing + adhesive thickness
Industry standards:
- ASTM D6988: Standard specification for polyethylene film (thickness in mils)
- ASTM D374: Method for measuring tape thickness (to 0.1 mil)
Example: A customer ordering "6-mil poly sheeting" for a concrete vapor barrier receives polyethylene film exactly 0.006″ (6 mils = 0.15 mm) thick, ensuring compliance with IRC building code.
4. Electronics and Printed Circuit Boards
PCB design and manufacturing is dominated by mil-based dimensions in the United States:
PCB design software (Altium, Eagle, KiCAD, OrCAD):
- Default grid spacing: 50 mils, 25 mils, 10 mils, 5 mils, 1 mil
- Component libraries use 100-mil pin spacing for through-hole parts
- Trace width and clearance rules specified in mils
Design rules and capabilities:
- Standard PCB fabrication (budget services):
- Minimum trace width: 6 mils
- Minimum spacing: 6 mils
- Via drill: 8-10 mils
- Copper weight: 1 oz (1.4 mils)
- Advanced PCB fabrication:
- Minimum trace/space: 3 mil / 3 mil
- Microvias: 4-6 mil drill
- HDI (high-density interconnect): sub-mil features
Copper thickness selection:
- 1 oz copper (1.4 mils): Standard for signal layers, adequate for currents <3A
- 2 oz copper (2.8 mils): Power planes, higher current capacity (5-10A per trace)
- 3-4 oz copper (4.2-5.6 mils): Power electronics, automotive
- Current-carrying capacity increases with thickness (more copper = less resistance = less heat)
PCB stackup (multilayer boards):
- 4-layer board example:
- Top copper: 1.4 mils (1 oz)
- Prepreg: 7 mils
- Inner layer 1 (ground): 1.4 mils
- Core: 47 mils
- Inner layer 2 (power): 1.4 mils
- Prepreg: 7 mils
- Bottom copper: 1.4 mils
- Total: 67 mils (1.7 mm)
Soldermask and silkscreen:
- Soldermask (green coating): 0.8-1.2 mils thickness
- Silkscreen (white text): 0.5-1 mil
- Surface finish (ENIG gold): 1-2 microinches (0.001-0.002 mil)
5. Wire Gauge and Cable Manufacturing
American Wire Gauge (AWG) is fundamentally based on diameter in mils:
AWG diameter formula:
- Each gauge step represents approximately a 1.123× change in diameter (10 steps = 1 decade = 10× area change)
- AWG 10 = 102 mils diameter
- AWG 20 = 32 mils diameter
- AWG 30 = 10 mils diameter
Wire insulation thickness (in mils over conductor diameter):
- Thin-wall insulation: 4-8 mils
- Standard insulation: 15-30 mils
- High-voltage insulation: 30-60+ mils
- Specification: "22 AWG with 10 mil insulation" = 25 mil conductor + 20 mil insulation total = 45 mil overall diameter
Magnet wire (enameled copper for motors, transformers):
- AWG 28-40 common for small coils
- Enamel coating: 0.5-2 mils depending on temperature rating
- Grade 1 (thinnest): 0.5-0.8 mil enamel
- Grade 2 (standard): 1-1.5 mil enamel
- Grade 3 (heavy build): 2-3 mil enamel
- Thicker enamel = better insulation, lower packing density in coil
Cable jacket thickness:
- Ethernet Cat6 cable jacket: 20-30 mils
- Power cord (SJOOW): 60-80 mils
- Mining cable: 125-250 mils (extreme abrasion resistance)
6. Sheet Metal and Gauge Systems
Sheet metal thickness is specified in gauge numbers, but actual thickness is in decimal inches (mils):
Manufacturer's Standard Gauge (steel):
- 10-gauge = 135 mils (0.1345″)
- 14-gauge = 75 mils (0.0747″)
- 20-gauge = 36 mils (0.0359″)
- 24-gauge = 24 mils (0.0239″)
Confusion and standardization issues:
- Gauge numbers are not universal: steel gauge ≠ aluminum gauge ≠ galvanized gauge
- Modern practice: Always specify in decimal inches (mils) to avoid ambiguity
- Example: "0.060″ aluminum" (60 mils) instead of "14-gauge aluminum"
HVAC ductwork:
- Residential ducts: 24-26 gauge (18-30 mils)
- Commercial ducts: 20-22 gauge (33-42 mils)
- Galvanized coating adds 2-5 mils to thickness
Automotive body panels:
- Hood outer skin: 28-30 mils (0.7-0.8 mm)
- Door outer skin: 26-28 mils
- Roof panel: 28-32 mils
- Frame rails: 90-120 mils (2.3-3.0 mm)
7. Quality Control and Standards Compliance
Mil-based specifications appear in thousands of ASTM, ANSI, SAE, and military standards:
ASTM coating standards:
- ASTM D3359: Adhesion of coatings (measured after cutting through coating, thickness in mils)
- ASTM D1186: Paint film thickness (magnetic gauges calibrated in mils)
- ASTM D6132: Nondestructive measurement of dry film thickness (mils)
Military specifications (MIL-SPEC):
- MIL-DTL-53030: Primer coating, epoxy, 2-3 mils DFT
- MIL-PRF-85285: Coating, polyurethane, aircraft, 1.5-2.5 mils
- Compliance requires thickness measurement at specified intervals
Building codes and construction:
- International Residential Code (IRC): Vapor retarders minimum 6 mils
- Roofing underlayment: Minimum thickness specifications in mils
- Window film (safety/security): 4-14 mils for various protection levels
Automotive and aerospace:
- SAE J1960: Brake hose specifications (wall thickness in inches/mils)
- AS9100 (aerospace quality): Dimensional inspections recorded in mils
- Engine bearing clearances: Specified in mils (e.g., 1.5-2.5 mils for main bearings)
Additional Unit Information
About Nanometer (nm)
1. How small is a nanometer?
A nanometer is extraordinarily small—one billionth of a meter (0.000000001 m). To grasp this scale: A human hair is about 80,000-100,000 nm wide, so you could fit 80,000-100,000 nanometers across a single hair. A sheet of paper is ~100,000 nm thick. The DNA double helix is 2 nm wide. A typical protein molecule is 5-50 nm. A single gold atom is ~0.3 nm diameter, so 1 nanometer spans approximately 3-4 atoms. If a nanometer were enlarged to 1 centimeter, a meter would stretch 10,000 kilometers—farther than the distance from New York to Tokyo. At this scale, quantum mechanical effects dominate: electrons behave as waves, particles can tunnel through barriers, and material properties become size-dependent.
2. How many nanometers are in a micrometer?
There are exactly 1,000 nanometers in 1 micrometer (μm). The relationship: 1 μm = 1,000 nm, or 1 nm = 0.001 μm. This factor of 1,000 comes from the metric prefix system: micro (μ) = 10⁻⁶ and nano (n) = 10⁻⁹, so 10⁻⁶ ÷ 10⁻⁹ = 10³ = 1,000. Examples: A typical bacterium (E. coli) is 2 μm long = 2,000 nm. A red blood cell is 7-8 μm diameter = 7,000-8,000 nm. A virus is 20-400 nm = 0.02-0.4 μm. Human hair is 80 μm = 80,000 nm. The nanometer-to-micrometer boundary (~100-1,000 nm) roughly separates the realm of individual molecules and nanoparticles (nm) from the realm of cells and microorganisms (μm).
3. Why are nanometers important in technology?
Nanometers are the scale at which quantum mechanical effects emerge, enabling revolutionary technologies. At 1-100 nm, materials exhibit size-dependent properties impossible to achieve in bulk: gold nanoparticles turn red; semiconductor quantum dots emit precise colors based on size; carbon nanotubes become stronger than steel. Semiconductor chips have shrunk to 3-5nm process nodes, packing billions of transistors into fingernail-sized dies—enabling smartphones, AI, cloud computing. Nanometer precision allows atomic layer deposition (building materials atom-by-atom), molecular diagnostics (detecting single protein molecules), targeted drug delivery (100nm nanoparticles accumulate in tumors), and metamaterials (nanoscale structures that bend light impossibly). The nanometer sits at the sweet spot: large enough to fabricate with advanced tools (electron beam lithography, STM manipulation), small enough to exploit quantum effects and interact with individual molecules—making it the frontier of 21st-century technology.
4. What's the difference between a nanometer and an angstrom?
A nanometer (nm) equals 10 angstroms (Å). The angstrom (1 Å = 0.1 nm = 10⁻¹⁰ meters) was historically used in atomic physics, chemistry, and crystallography because atomic diameters and chemical bond lengths conveniently fall in the 1-5 Å range (hydrogen atom: ~1 Å, carbon-carbon bond: 1.54 Å). However, the angstrom is not an SI unit, and modern scientific practice favors nanometers and picometers. Example: The diameter of a DNA double helix is 2 nm = 20 Å. The spacing between DNA base pairs is 0.34 nm = 3.4 Å. A silicon atom is 0.21 nm = 2.1 Å diameter. While older papers and crystallography software often report structures in angstroms, nanometers are now standard in nanotechnology, materials science, and most contemporary research. If you see Å, just divide by 10 to convert to nanometers.
5. Can you see something that's 1 nanometer?
No, you cannot see 1 nanometer with any optical microscope, and barely even with your eyes' theoretical maximum resolution. Human eyes can resolve ~50-100 micrometers (50,000-100,000 nm) at best. Optical microscopes are limited by the diffraction limit—approximately half the wavelength of light used. Visible light ranges 400-700 nm, so the best optical resolution is ~200-300 nm (using UV light and oil immersion). To "see" 1 nm structures, you need: Transmission Electron Microscope (TEM): Uses electron beams (wavelength ~0.01 nm at high voltage), achieving 0.1-1 nm resolution—can image individual atoms. Scanning Tunneling Microscope (STM) or Atomic Force Microscope (AFM): "Feel" surfaces by scanning a sharp tip (1-atom-wide apex) across the sample, mapping topography with sub-nanometer precision. So yes, we can "see" nanometer and sub-nanometer features, but not with light—we use electrons or physical probes.
6. Why are modern chips called "3nm" or "5nm" when features aren't actually that small?
Modern process node names (3nm, 5nm, 7nm) are marketing terms reflecting relative density improvements, not actual physical dimensions. Historically, process nodes indicated the smallest feature size (e.g., Intel's 130nm process in 2001 had ~130nm gate lengths). But as scaling slowed and 3D transistor designs (FinFETs) emerged, the relationship broke down. Today: A "5nm" chip from TSMC might have gate lengths ~20-30nm, metal pitch ~30-40nm, and the tightest pitch structures ~24-28nm. The "5nm" refers roughly to an equivalent density compared to hypothetical scaling trends. A "3nm" chip is denser than "5nm," but actual dimensions are larger than 3nm. Why keep the naming? Industry convention, marketing (smaller number sounds more advanced), and rough correlation with transistor density. Different manufacturers' "5nm" may differ significantly. Bottom line: Process nodes indicate generation and relative performance/density, not literal nanometer measurements.
7. What's the smallest thing ever manipulated by humans?
Humans have manipulated individual atoms (~0.1-0.3 nm), the smallest stable units of matter. 1989: IBM scientists used a Scanning Tunneling Microscope (STM) to arrange 35 xenon atoms to spell "IBM" on a nickel surface—the first atomic-scale manipulation. 1990s-present: Researchers built molecular structures atom-by-atom: molecular gears, switches, quantum corrals (rings of atoms to confine electrons). 2012: Physicists stored 1 bit of data in a single holmium atom (~0.25 nm diameter) using magnetic orientation. Subatomic particles: Particle accelerators (LHC) manipulate protons (~0.0016 nm diameter) and study quarks (~10⁻³ to 10⁻⁴ nm, though quarks can't be isolated). Quantum engineering: Controlling individual electron spins, photon states, and qubits for quantum computing. So while atoms (~0.1-0.3 nm) are the smallest stable structures we manipulate routinely, we probe and control phenomena down to 10⁻⁵ nm scales in particle physics.
8. How does nanotechnology differ from regular technology?
Nanotechnology operates at 1-100 nm scale where quantum mechanical effects become significant and surface-area-to-volume ratios are enormous, enabling properties impossible in bulk materials. Differences: Scale: Nanotech manipulates individual molecules, atoms, or nanostructures; regular tech uses bulk materials. Quantum effects: At nanoscale, quantum tunneling, quantized energy levels, and wave-particle duality dominate; bulk materials follow classical physics. Size-dependent properties: Gold nanoparticles (5-50 nm) are red/purple and reactive; bulk gold is yellow and inert. Quantum dots (2-10 nm) emit precise colors tuned by size—impossible with bulk semiconductors. Surface area: Nanoparticles have immense surface area relative to volume, making them superb catalysts, drug carriers, and sensors. Bottom-up assembly: Nanotech often uses molecular self-assembly or atom-by-atom fabrication; traditional manufacturing is top-down (machining, cutting). Applications: Nanotech enables mRNA vaccines (lipid nanoparticles), 3nm computer chips, targeted cancer therapy, and quantum computing—revolutionary advances impossible with conventional approaches.
9. Is nanotechnology safe?
Nanotechnology safety is highly material-specific—some nanomaterials are safe, others pose risks. Concerns: 1) Toxicity: Some nanoparticles (carbon nanotubes, certain metal oxides) can damage cells, cause inflammation, or penetrate biological barriers (blood-brain barrier). Silver nanoparticles, widely used in antimicrobial products, can harm aquatic life. 2) Environmental persistence: Nanoparticles may accumulate in ecosystems with unknown long-term effects. 3) Inhalation: Ultrafine airborne nanoparticles (~10-100 nm) penetrate deep into lungs, potentially causing respiratory issues. Safety measures: Extensive testing: New nanomaterials undergo toxicology studies before commercial use. Regulation: FDA, EPA, EU regulate nanomaterials in drugs, food, cosmetics, and industrial applications. Encapsulation: Many nanoparticles (e.g., in sunscreen, food) are embedded in matrices, preventing release. Established safety: Some nanomaterials are demonstrably safe (titanium dioxide and zinc oxide in sunscreen used for decades; lipid nanoparticles in mRNA vaccines tested extensively). Conclusion: Nanotech isn't universally safe or dangerous—each material requires careful evaluation.
10. How do semiconductor fabs create nanometer-scale features?
Modern semiconductor fabrication uses photolithography with extreme precision and multi-step patterning. Extreme Ultraviolet (EUV) Lithography: Uses 13.5 nm wavelength light (generated by tin plasma) to pattern features. Wavelength is much smaller than older 193 nm UV lithography, enabling finer patterns. Process: 1) Coat silicon wafer with photoresist (~50-100 nm layer). 2) Project circuit pattern onto resist using EUV light through precision optics. 3) Exposed resist dissolves, leaving pattern. 4) Etch exposed silicon, deposit materials, etc. 5) Repeat hundreds of times (modern chips: 20-25+ mask layers). Multi-patterning: Single exposure can't achieve tightest pitches, so features are created through multiple aligned exposures (self-aligned double patterning, etc.). Atomic Layer Deposition (ALD): Deposits ultra-thin films (~0.1-1 nm precision) for gates, insulators. FinFET 3D transistors: Vertical silicon fins (~5-7 nm wide) provide better gate control at nanoscale. Extreme precision: Alignment accuracy: ~1-2 nm. Temperature control: ±0.01°C. Cleanrooms: <1 particle/cubic meter. Took decades of R&D and billions in equipment development to achieve 3-5nm nodes.
11. What's the limit of miniaturization in computer chips?
Miniaturization faces several fundamental limits expected to halt around 1-2 nm nodes (late 2020s-early 2030s): 1) Atomic scale: Silicon atoms are ~0.21 nm diameter. At 1-2 nm features, structures are just 5-10 atoms wide—difficult to control dopant placement and variability. 2) Quantum tunneling: Electrons can "tunnel" through barriers < 1-2 nm thick, causing leakage current and preventing transistors from turning off. 3) Heat dissipation: Power density in chips approaches limits of cooling technology. Shrinking further increases current density and heat. 4) Manufacturing precision: Atomic-level variations affect device performance. Placing individual dopant atoms precisely is extremely difficult. Beyond silicon: Future options include: New materials (carbon nanotubes, graphene, 2D materials). 3D stacking (vertical integration). New transistor architectures (gate-all-around FETs, tunnel FETs). Beyond CMOS (quantum computing, photonic computing, neuromorphic chips). Moore's Law (doubling transistor count every 2 years) is already slowing. The 1 nm node may be the practical limit for silicon, necessitating entirely new computing paradigms.
12. Can nanotechnology create molecular machines?
Yes! Molecular machines—nanometer-scale structures that perform mechanical work—exist naturally and are being engineered artificially. Natural molecular machines: Ribosomes (~20 nm): Synthesize proteins, translating mRNA into amino acid chains (Nobel Prize 2009 for structure determination). ATP synthase (~10 nm): Rotary motor in mitochondria, spins at ~100 Hz to produce ATP (cellular energy currency). Kinesin motors (~10 nm): "Walk" along microtubules, transporting cargo within cells. DNA polymerase: Copies DNA, moving along strands, proof-reading, and assembling nucleotides. Synthetic molecular machines (Nobel Prize in Chemistry 2016): Molecular motors: Light-driven rotors, chemically-driven linear motors (synthesized by Fraser Stoddart, Jean-Pierre Sauvage, Ben Feringa). DNA origami machines: Programmable nanoscale structures that fold, unfold, or grasp objects. Potential applications: Nanoscale drug delivery, molecular computing, self-assembling materials, targeted cell repair. Challenges: Operating in biological environments, controlling motion precisely, scaling up production. Molecular machines are early-stage but represent frontier of nanotechnology.
About Mil/Thou (mil)
Is a mil the same as a millimeter?
No—they are very different units, despite similar names.
- 1 mil (imperial) = 0.001 inches = 0.0254 mm = 25.4 micrometers
- 1 millimeter (metric) = 0.001 meters = 39.37 mils
Key difference: 1 millimeter is approximately 40 times larger than 1 mil. Confusing these units results in massive errors (40× too thick or thin).
Origin of confusion: "Mil" sounds like an abbreviation for "millimeter," but it actually comes from the Latin "mille" (thousand), meaning one thousandth of an inch. In some non-English languages, "mil" or "mil." is used as slang for millimeter, compounding confusion in international contexts.
Prevention: Always write units explicitly—"6 mils (0.15 mm)" or "0.2 mm (7.9 mils)"—in international specifications.
What does 'thou' mean, and is it the same as a mil?
Yes—"thou" and "mil" are exactly the same measurement: one thousandth of an inch (0.001″).
Regional differences:
- "Mil" is standard in American technical documentation, industry standards (ASTM, ANSI, SAE), and scientific publications.
- "Thou" is common in British English shop-floor terminology, machining, and colloquial engineering speech.
Etymology:
- "Mil" comes from Latin "mille" (thousand)
- "Thou" is an abbreviation of "thousandth" (of an inch)
Usage examples:
- American engineer: "Tolerance is plus or minus five mils."
- British machinist: "Take another two thou off the diameter."
- Both mean exactly: 0.005″ and 0.002″ respectively.
Documentation practice: Technical drawings and specifications predominantly use "mil" or the decimal notation (0.001″), while "thou" appears more in verbal communication and informal notes.
How many mils are in an inch?
Exactly 1,000 mils = 1 inch by definition.
The mil is defined as one thousandth of an inch:
- 1 mil = 0.001″
- 1 inch = 1,000 mils
Common fractions converted to mils:
- 1/2″ = 500 mils
- 1/4″ = 250 mils
- 1/8″ = 125 mils
- 1/16″ = 62.5 mils
- 1/32″ = 31.25 mils
- 1/64″ = 15.625 mils
This decimal subdivision makes arithmetic much easier than traditional fractional inches (no need to find common denominators).
Why do we still use mils instead of millimeters?
Several practical and historical reasons explain the mil's persistence in American industry despite global metrication:
1. Legacy infrastructure (strongest reason):
- Billions of dollars invested in tooling, fixtures, gauges, and manufacturing equipment calibrated in inches/mils
- Converting existing designs and technical documentation is prohibitively expensive and risky
- Critical industries (aerospace, defense, medical) have decades of proven designs that cannot be easily converted
2. Compatibility and interchangeability:
- Replacing a part requires exact dimensional compatibility
- Mixed mil/metric systems in a single product line risk catastrophic errors (e.g., 1999 Mars Climate Orbiter loss due to metric/imperial confusion)
- Entire supply chains (thousands of vendors) must convert simultaneously for compatibility
3. Established standards:
- American Wire Gauge (AWG) is based on mils
- ASTM, ANSI, SAE, and military specifications (MIL-SPEC) use mils
- Rewriting thousands of standards documents is a monumental undertaking
4. Practical advantages in some contexts:
- PCB design: 100-mil (0.1″) pin spacing is convenient, memorable, and grid-friendly
- Engineering calculations: Tolerances like "±5 mils" are intuitive to experienced engineers
- Decimal-inch system avoids fractional arithmetic while maintaining imperial base
5. Economic inertia:
- No compelling economic driver for conversion in purely domestic manufacturing
- Cost of conversion (training, documentation, tooling) outweighs benefits in mature industries
6. Cultural and educational factors:
- American engineers trained in decimal-inch system for generations
- Familiarity breeds efficiency—experienced machinists "think in mils"
Counterpoint: Industries with strong international ties (automotive, consumer electronics) increasingly use dual dimensioning (both mils and mm) or have shifted to metric. New designs often start in metric, but maintenance of existing imperial products ensures mils remain relevant for decades.
How do I convert mils to micrometers (microns)?
Multiply mils by 25.4 to get micrometers (μm):
Formula: μm = mils × 25.4
Examples:
- 1 mil × 25.4 = 25.4 μm
- 5 mils × 25.4 = 127 μm
- 10 mils × 25.4 = 254 μm
- 100 mils × 25.4 = 2,540 μm (= 2.54 mm)
Reverse conversion (micrometers to mils): Divide by 25.4
Formula: mils = μm ÷ 25.4
Examples:
- 50 μm ÷ 25.4 = 1.97 mils (≈ 2 mils)
- 100 μm ÷ 25.4 = 3.94 mils (≈ 4 mils)
- 250 μm ÷ 25.4 = 9.84 mils (≈ 10 mils)
Why 25.4? Because 1 inch = 25.4 mm exactly (by the 1959 international agreement), and 1 mil = 0.001 inch, so:
- 1 mil = 0.001 inch × 25.4 mm/inch = 0.0254 mm = 25.4 μm
Practical use: Coating thickness specifications often appear in both units:
- "Apply to 5 mils (127 μm) dry film thickness"
- Ensures international suppliers understand the requirement
What is 1 mil in metric units?
1 mil = 25.4 micrometers (μm) = 0.0254 millimeters (mm) exactly.
Complete metric equivalents:
- 1 mil = 25.4 μm (most common metric expression for precision work)
- 1 mil = 0.0254 mm (less common, but useful for larger scales)
- 1 mil = 0.0000254 meters
- 1 mil = 25,400 nanometers (semiconductor/optics context)
Reverse:
- 1 micrometer (μm) = 0.03937 mil (≈ 1/25 mil)
- 1 millimeter (mm) = 39.37 mils (≈ 40 mils for quick estimation)
Why exactly 25.4? The 1959 international yard and pound agreement defined:
- 1 inch = 25.4 mm exactly
- Therefore: 1 mil = 0.001 inch = 25.4 μm exactly
This is not an approximation—it's the legal definition linking imperial and metric systems.
How thick is 4 mils?
4 mils = 0.004 inches = 0.1 mm (100 micrometers) — about the thickness of standard printer paper.
Everyday comparisons for 4 mils:
- Two sheets of standard copy paper stacked (each ~4 mils)
- Human hair is roughly 2× thicker (70-100 mils vs. 4 mils)
- Credit card is roughly 7.5× thicker (30 mils vs. 4 mils)
- Fingernail is roughly 5-7× thicker (20-30 mils)
Common uses of 4-mil thickness:
- Printer/copy paper (20 lb bond): 3.5-4.5 mils
- Automotive paint (single coat): 1.5-2 mils base + 1.5-2 mils clear = 4-5 mils total
- Polyethylene sheeting (light-duty drop cloths): 3-4 mils
- House paint (exterior, dry film): 1.5-2 coats × 2 mils each = 4-5 mils
Feeling 4 mils: Too thin to feel accurately with fingers—requires calipers or micrometer to measure precisely.
What is considered a tight tolerance in mils?
"Tight" tolerances depend on the manufacturing process and application, but general industry standards are:
General fabrication and commercial machining:
- Loose tolerance: ±10-20 mils (±0.010-0.020″)
- Standard tolerance: ±5 mils (±0.005″)
- Tight tolerance: ±1-2 mils (±0.001-0.002″)
Precision machining:
- Standard: ±1 mil (±0.001″)
- Tight: ±0.5 mil (±0.0005″)
- Very tight: ±0.1-0.2 mil (±100-200 microinches)
Ultra-precision (grinding, diamond turning):
- Tight: ±0.05 mil (±50 microinches = ±1.3 μm)
- Extremely tight: ±0.01 mil (±10 microinches = ±0.25 μm)
Application examples:
- Engine piston fit: 1-3 mils clearance (0.001-0.003″) — critical for sealing and oil retention
- Bearing journals: ±0.5 mil tolerance — affects bearing life and performance
- Hydraulic valve spool: 0.5-1 mil clearance — controls internal leakage
- Gauge blocks (Grade 0): ±0.05 mil (±50 microinches) — calibration standard
- Optical lens mounts: ±0.1 mil — affects focus and alignment
Cost impact: Tighter tolerances require:
- More precise equipment (CNC machining centers, grinders)
- Slower machining speeds and feeds
- More frequent inspection
- Skilled machinists
- Climate-controlled environment (for extreme precision)
Rule of thumb: Each 10× reduction in tolerance (e.g., ±10 mils → ±1 mil → ±0.1 mil) roughly doubles or triples machining cost.
How do you measure thickness in mils?
Several tools measure thickness in mils, depending on the material and access:
1. Micrometer (most common for solid parts):
- Handheld precision tool with anvil and spindle
- Resolution: 0.001″ (1 mil) for standard micrometers; 0.0001″ (0.1 mil) for digital or vernier micrometers
- How to use: Place object between anvil and spindle, turn thimble until it contacts with light resistance, read measurement
- Accuracy: ±0.0001″ (±0.1 mil) or better when calibrated
- Best for: Solid materials (sheet metal, plastic, gaskets, wire)
2. Digital calipers:
- Resolution: Typically 0.001″ (1 mil) or 0.01 mm
- Easier to read than dial calipers (digital display)
- Less precision than micrometers (±1-2 mils accuracy)
- Best for: Quick measurements, larger parts, non-critical dimensions
3. Coating thickness gauges (for paint/plating):
- Magnetic gauges (ferrous substrates): Reed switch or Hall effect sensor detects distance through non-magnetic coating
- Eddy current gauges (non-ferrous substrates): Measures impedance change due to coating thickness
- Ultrasonic gauges: Sound wave reflection for non-metallic coatings or any substrate
- Resolution: Typically 0.1 mil (2.5 μm) to 1 mil depending on model
- Best for: Paint, powder coating, galvanizing, plating, anodizing on metal substrates
4. Wet film thickness gauges (paint application):
- Notch/comb gauges: Comb with graduated teeth (2, 4, 6, 8, 10 mils)
- How to use: Insert comb perpendicular into wet paint; highest clean tooth (no paint) indicates thickness
- Resolution: Depends on tooth spacing (typically 2 mil increments)
- Best for: Field inspection during painting to ensure proper application
5. Dial indicators (for comparing thickness):
- Measures variation rather than absolute thickness
- Place part on reference surface, indicator plunger contacts top
- Resolution: 0.001″ (1 mil) or 0.0001″ (0.1 mil) for precision models
- Best for: Checking flatness, parallelism, thickness variation across a surface
6. Optical/laser micrometers (non-contact):
- Laser beam measures shadow of object passing through
- Resolution: Sub-mil (0.01-0.1 mil) depending on model
- Best for: Soft materials (rubber, foam) or high-speed production inspection (wire, cable)
Calibration: All precision measuring tools require regular calibration against gauge blocks or calibration standards to maintain accuracy.
Why is PCB design done in mils?
PCB (printed circuit board) design uses mils primarily due to historical legacy and practical convenience in American electronics manufacturing:
1. Component standards based on 100-mil spacing:
- Through-hole components (resistors, ICs, connectors) were standardized with 0.1″ (100 mil) pin spacing in the 1950s-1970s
- Dual in-line packages (DIP): Pins spaced at 100 mil intervals
- Perfboard and breadboards: 100 mil grid for prototyping
- This 100-mil standard became embedded in component libraries and CAD software
2. PCB design grid convenience:
- Grid snapping: CAD software uses grids (50 mil, 25 mil, 10 mil, 5 mil, 1 mil)
- 100 mil grid allows easy component placement aligned with standard pin spacing
- Fractional grids: 50 mil (0.05″), 25 mil (0.025″) for routing between pins
- Metric equivalents (2.54 mm, 1.27 mm, 0.635 mm) are awkward, non-round numbers
3. Trace width and spacing in convenient numbers:
- Typical design rules: 6 mil trace / 6 mil space (easier to remember than "0.15 mm / 0.15 mm")
- High-current traces: 15 mil, 20 mil, 30 mil widths (round numbers)
- Advanced designs: 3 mil / 3 mil minimum capability
4. Standard PCB thickness:
- 62 mils (1.57 mm) is the industry-standard board thickness—originated in imperial measurements
- Thinner boards: 31 mils (0.8 mm), 47 mils (1.2 mm)
- Thicker boards: 93 mils (2.4 mm), 125 mils (3.2 mm)
5. Copper weight in oz/ft² naturally maps to mils:
- 1 oz copper = 1.4 mils thick (34.8 μm)
- 2 oz copper = 2.8 mils thick
- Easy calculation for impedance and current capacity
6. Legacy and tool compatibility:
- Enormous library of existing designs, footprints, and components in mil units
- PCB CAD software (Altium, Eagle, OrCAD, KiCAD) default to mils in U.S. installations
- Converting to metric risks errors and incompatibility with legacy designs
Modern trend: Some international PCB design now uses metric (especially in Europe and Asia), but American designs and military/aerospace specs remain overwhelmingly mil-based. Many CAD tools support dual dimensioning to bridge both systems.
Are mils still relevant today, or is it an obsolete unit?
Mils are absolutely still relevant and widely used in American manufacturing, despite global metrication trends. The unit is not obsolete—it remains the standard in several major industries:
Industries actively using mils today (2020s):
1. Printed circuit board (PCB) and electronics manufacturing:
- Trace widths, spacing, and via sizes specified in mils
- Component libraries and footprints use 100-mil pin spacing
- Standard fabrication capabilities: "6 mil trace / 6 mil space"
2. Aerospace and defense:
- Military specifications (MIL-SPEC) use mils for tolerances and coating thickness
- Legacy aircraft designs (Boeing, Lockheed Martin) remain in decimal-inch/mil system
- Interchangeable parts for decades-old platforms require dimensional consistency
3. Precision machining and manufacturing:
- Tolerances routinely specified in mils (±1 mil, ±5 mil)
- Micrometer readings in decimal inches (thousandths)
- CNC programming often in inches/mils in American shops
4. Coating and painting industries:
- ASTM and SSPC standards specify dry film thickness (DFT) in mils
- Paint thickness gauges calibrated in mils
- Industrial specifications: "8-10 mils total coating system"
5. Plastic film and flexible packaging:
- Film thickness: "6-mil poly sheeting," "4-mil polyester film"
- ASTM standards for plastic film thickness use mils
6. Wire and cable manufacturing:
- American Wire Gauge (AWG) based on diameter in mils
- Insulation thickness specified in mils over conductor
7. Sheet metal fabrication:
- Actual thickness often specified in decimal inches (mils) to avoid gauge confusion
- "0.063″ aluminum" (63 mils) instead of ambiguous "14-gauge"
Why mils persist:
- Billions in tooling and infrastructure calibrated in imperial units
- Legacy designs: Decades of proven engineering in mils cannot be easily converted
- Risk avoidance: Metric/imperial conversion errors are costly and dangerous (Mars Climate Orbiter)
- Supply chain compatibility: Entire ecosystems of suppliers and manufacturers use consistent units
- No economic driver: Purely domestic manufacturing has little incentive to convert
Metric adoption: Global companies (automotive, consumer electronics) increasingly use dual dimensioning (both mils and mm) or shift new designs to metric, but maintenance and support of existing products ensures mils remain relevant for decades.
Conclusion: Mils are actively used, not obsolete, and will remain standard in American manufacturing for the foreseeable future—especially in aerospace, defense, electronics, and precision machining.
What's the difference between a mil and a milliradian?
Completely different units from different measurement domains—they only share a similar name:
Mil (length):
- Unit of length = 0.001 inches (one thousandth of an inch)
- Used in manufacturing, coating thickness, electronics, tolerances
- Example: "The coating is 5 mils thick."
Milliradian (angular measurement):
- Unit of angle = 0.001 radians ≈ 0.0573 degrees
- Used in artillery, ballistics, marksmanship, optics, surveying
- Example: "The rifle scope adjustment is 0.1 milliradian per click."
No conversion between them—they measure fundamentally different things (distance vs. angle).
Confusing terminology: In military and shooting contexts, "mil" is often shorthand for milliradian (angular mil), while in manufacturing, "mil" always means 0.001 inch (linear mil). Context determines meaning.
Additional angular "mil" units (adding to confusion):
- NATO mil (milliradian): 1/1000 radian ≈ 0.0573°
- Swedish/metric mil: 1/6000 of a circle ≈ 0.06° (slightly larger than milliradian)
- Artillery mil (historical): 1/6400 of a circle ≈ 0.05625°
Summary: Unless you're discussing ballistics or optics, "mil" refers to 0.001 inch in American industry and manufacturing.
Conversion Table: Nanometer to Mil/Thou
| Nanometer (nm) | Mil/Thou (mil) |
|---|---|
| 0.5 | 0 |
| 1 | 0 |
| 1.5 | 0 |
| 2 | 0 |
| 5 | 0 |
| 10 | 0 |
| 25 | 0.001 |
| 50 | 0.002 |
| 100 | 0.004 |
| 250 | 0.01 |
| 500 | 0.02 |
| 1,000 | 0.039 |
People Also Ask
How do I convert Nanometer to Mil/Thou?
To convert Nanometer to Mil/Thou, enter the value in Nanometer in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our length converter page to convert between other units in this category.
Learn more →What is the conversion factor from Nanometer to Mil/Thou?
The conversion factor depends on the specific relationship between Nanometer and Mil/Thou. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.
Can I convert Mil/Thou back to Nanometer?
Yes! You can easily convert Mil/Thou back to Nanometer by using the swap button (⇌) in the calculator above, or by visiting our Mil/Thou to Nanometer converter page. You can also explore other length conversions on our category page.
Learn more →What are common uses for Nanometer and Mil/Thou?
Nanometer and Mil/Thou are both standard units used in length measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our length converter for more conversion options.
For more length conversion questions, visit our FAQ page or explore our conversion guides.
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📚 How to Convert Units
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🔢 Conversion Formulas
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⚖️ Metric vs Imperial
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All Length Conversions
Other Length Units and Conversions
Explore other length units and their conversion options:
- Meter (m) • Nanometer to Meter
- Kilometer (km) • Nanometer to Kilometer
- Hectometer (hm) • Nanometer to Hectometer
- Decimeter (dm) • Nanometer to Decimeter
- Centimeter (cm) • Nanometer to Centimeter
- Millimeter (mm) • Nanometer to Millimeter
- Inch (in) • Nanometer to Inch
- Foot (ft) • Nanometer to Foot
- Yard (yd) • Nanometer to Yard
- Mile (mi) • Nanometer to Mile
Verified Against Authority Standards
All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.
National Institute of Standards and Technology — Official US standards for length measurements
Bureau International des Poids et Mesures — International System of Units official documentation
Last verified: December 3, 2025