Point (Typography) to Mil/Thou Converter
Convert points to mils with our free online length converter.
Quick Answer
1 Point (Typography) = 13.888898 mils
Formula: Point (Typography) × conversion factor = Mil/Thou
Use the calculator below for instant, accurate conversions.
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Point (Typography) to Mil/Thou Calculator
How to Use the Point (Typography) to Mil/Thou Calculator:
- Enter the value you want to convert in the 'From' field (Point (Typography)).
- 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 Point (Typography) to Mil/Thou: Step-by-Step Guide
Converting Point (Typography) to Mil/Thou involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Point (Typography) = 13.8889 milsExample Calculation:
Convert 10 points: 10 × 13.8889 = 138.889 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.
Not for professional use. Results should be verified before use in any critical application. View our Terms of Service for more information.
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View all Length conversions →What is a Point (Typography) and a Mil/Thou?
The Desktop Publishing Point
The modern typographic point is defined as exactly 1/72 of an international inch. This creates the mathematically convenient relationship:
- 1 point (pt) = 1/72 inch = 0.013888... inches
- 1 point = 0.352777... millimeters
- 72 points = 1 inch (exactly)
- 1 inch = 25.4 mm (by international definition)
This definition, known as the PostScript point or DTP point (Desktop Publishing point), was established by Adobe Systems in the 1980s and has become the universal standard for all modern typography.
The Em Square and Font Height
When we say "12 pt font," we're technically measuring the em square—the metal block that held the physical letter in traditional typesetting. This em square includes:
- Ascenders: Parts of letters extending above the baseline (like the top of 'h' or 'b')
- Descenders: Parts extending below the baseline (like the tail of 'g' or 'y')
- Built-in spacing: Extra vertical space above and below letters
This means 12 pt text doesn't have letters exactly 1/6 inch tall—the actual visible letter height (called x-height) is typically 60-70% of the point size, with the rest being built-in spacing. This spacing prevents lines of text from touching each other.
Points vs. Picas
Typography traditionally pairs the point with the pica:
- 1 pica = 12 points = 1/6 inch
- 6 picas = 1 inch
- 1 pica ≈ 4.233 mm
Professional designers often measure larger typographic elements in picas. For example, a column width might be "20 picas" (3.33 inches) rather than "240 points." The pica provides a more manageable unit for page layout dimensions while maintaining exact mathematical relationships.
Historical Point Systems (Pre-Digital)
Before the DTP point standardization, multiple incompatible point systems existed:
Didot Point (Continental Europe):
- 1 Didot point ≈ 0.3759 mm
- Based on the French pied du roi (royal foot)
- Approximately 67.55 Didot points per inch
- Still occasionally referenced in European historical printing contexts
American/British Pica Point:
- 1 pica point ≈ 0.351459 mm
- 72.27 points per inch (not exactly 72!)
- Derived from metal type casting standards
- Also called the "Anglo-American point"
Fournier Point (Early French):
- Pierre Simon Fournier's original 1737 system
- Approximately 0.348 mm
- 72.989 points per French royal inch
- Largely replaced by Didot system by 1800
The digital revolution eliminated these variations. Today, when anyone uses "point" in typography, they mean the 1/72-inch DTP point unless explicitly stated otherwise.
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 Point (Typography) is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Mil/Thou belongs to the imperial/US customary system.
History of the Point (Typography) and Mil/Thou
Early Typography: The Cicero and Finger-Width (1400s-1700s)
Early European printing used inconsistent measurements based on:
- The cicero: A unit based on the line width of a specific typeface (Cicero type), varying by region
- Local inches and feet: Each region had different inch definitions
- Finger widths and eyeball estimates: Printers adjusted type spacing by hand
This inconsistency made it nearly impossible to share typeface designs or maintain consistency across print shops.
Pierre Simon Fournier: The First Point System (1737)
French typefounder Pierre Simon Fournier le Jeune published "Table des proportions" (1737), introducing the first systematic point system:
- Based the point on the French royal inch (pouce du roi)
- Divided the inch into 72 points (a number divisible by many factors: 2, 3, 4, 6, 8, 9, 12)
- Created 20 standardized font sizes
- Named sizes after musical terms (e.g., "Petit-Canon," "Gros-Parangon")
Fournier's system brought mathematical precision to typography for the first time, allowing typefounders to create consistent, proportional type families.
François-Ambroise Didot: The Didot Point (1783)
François-Ambroise Didot, another French typefounder, refined Fournier's system by basing measurements on the pied du roi (royal foot):
- 1 Didot point = 1/72 of 1/12 of the pied du roi ≈ 0.3759 mm
- Larger than Fournier's point (about 7% bigger)
- Created the cicero as 12 Didot points
- Established type size naming still used today (e.g., corps 8, corps 12)
The Didot system became the standard across Continental Europe and remains influential in French and German typography traditions. Some European printing specifications still reference "Didot" even today when discussing historical typography.
American and British Variations (1800s)
The 19th century saw typography spread across the English-speaking world, but without international standards:
American Point System (established c. 1886):
- Created by the United States Type Founders Association
- Based on the pica: 1 pica = 0.166 inches
- Therefore: 1 point = 0.166/12 ≈ 0.013837 inches
- Result: approximately 72.27 points per inch
British Imperial Point:
- Similar to American system but based on British imperial inch
- Also approximately 72.27 points per inch
- Created incompatibilities when Britain and US used different inch definitions before 1959
This proliferation of standards created international printing chaos. A "12 point" font in France was noticeably different from "12 point" in Britain or America.
Adobe PostScript: The Digital Revolution (1982-1985)
The desktop publishing revolution began when Adobe Systems developed PostScript, a page description language for laser printers:
John Warnock and Charles Geschke (Adobe founders) faced a choice: adopt historical point systems with fractional relationships to inches, or create a new, mathematically clean standard.
They chose simplicity: 1 point = exactly 1/72 inch
This decision meant:
- Easy calculation: multiply by 72 to convert inches to points
- Clean pixel mapping on early displays (72 DPI screens made 1 point = 1 pixel)
- No fractional arithmetic in computer calculations
- Complete break from historical confusion
Apple LaserWriter and Macintosh (1985)
Apple Computer licensed Adobe PostScript for the Macintosh computer and LaserWriter printer (launched January 1985):
- First affordable desktop publishing system
- 72 DPI screen resolution matched PostScript's 72 points/inch
- Onscreen "What You See Is What You Get" (WYSIWYG): Text appeared on screen at the exact size it would print
- Revolutionary for designers: no more calculating conversions
The LaserWriter cost $7,000 (expensive but far cheaper than typesetting equipment costing $50,000+), making professional typography accessible to small businesses and independent designers.
Industry Standardization (1985-1995)
The DTP point rapidly became universal:
1987: Adobe releases Adobe Illustrator and Photoshop (1990), both using PostScript points
1987: PageMaker (Aldus, later Adobe) becomes industry-standard layout software
1990s: Microsoft adopts 72 points/inch in Word, PowerPoint, Publisher
1996: CSS (Cascading Style Sheets) defines the pt unit as 1/72 inch for web typography
2000s: All professional design software (InDesign, Quark, CorelDRAW) standardizes on DTP point
By 2000, the historical Didot and pica points had effectively vanished from active use. The DTP point achieved something remarkable: complete global standardization of a measurement unit in just 15 years.
Modern Digital Era (2000-Present)
Today's typography operates in a world of complete point standardization:
- Print design: All software uses 72 pt/inch
- Web design: CSS
ptunits defined as 1/72 inch (thoughpxandemare more common online) - Mobile apps: iOS, Android use point-based typography systems
- E-readers: Kindle, Apple Books use point-based font sizing
- Office software: Word, Google Docs, Apple Pages all use identical point measurements
The point has become so universal that most designers under 40 have never encountered historical point systems. The DTP point is simply "the point."
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: points vs mils
Explore the typical applications for both Point (Typography) (imperial/US) and Mil/Thou (imperial/US) to understand their common contexts.
Common Uses for points
1. Document Typography and Word Processing
Body Text Standards:
- 10-12 pt: Standard body text for business documents, reports, letters
- 11 pt: Often considered optimal for printed books (balance of readability and page economy)
- 12 pt: Default in Microsoft Word, Google Docs; universally acceptable for any document
- 14 pt: Large print books for readers with visual impairments
Heading Hierarchies: Professional documents typically use 3-5 heading levels with systematic point size progression:
- H1 (Title): 18-24 pt, bold
- H2 (Major sections): 16-18 pt, bold
- H3 (Subsections): 14-16 pt, bold
- H4 (Minor subsections): 12-14 pt, bold or italic
- Body text: 10-12 pt, regular
This creates clear visual hierarchy while maintaining readability.
2. Professional Graphic Design and Layout
Adobe Creative Suite Standards:
- InDesign: All text boxes, frames, and measurements in points
- Illustrator: Artboard rulers can display points; all typography in points
- Photoshop: Type tool uses points by default
Print Design Specifications:
- Business cards: Names typically 14-18 pt, contact info 8-10 pt
- Brochures: Headlines 24-36 pt, body text 9-11 pt
- Posters: Titles 48-144+ pt depending on viewing distance
- Magazine layouts: Body 9-10 pt (smaller for dense content), headlines 18-48 pt
Grid Systems: Many designers use point-based grids: 12 pt baseline grids ensure consistent vertical rhythm across pages.
3. Web Typography (CSS)
CSS supports points, though pixels and ems are more common for responsive design:
body {
font-size: 12pt; /* Equivalent to 16px at 96 DPI */
}
h1 {
font-size: 24pt; /* Prints at exactly 1/3 inch tall */
}
@media print {
body { font-size: 11pt; } /* Optimize for printed output */
}
Print Stylesheets: Points are ideal for @media print CSS rules since they translate directly to physical printed size.
Fixed Layouts: PDF generators and print-to-web applications often use point-based layouts for predictable output.
4. Font Design and Development
Em Square Definition:
- Font designers work within an em square measured in points
- Traditionally 1000 or 2048 units per em square (OpenType fonts)
- Defines the bounding box for all characters
Typeface Specifications:
- X-height: Ratio of lowercase 'x' height to full em square (typically 0.5-0.6)
- Cap height: Uppercase letter height (typically 0.65-0.75 of em square)
- Ascenders/descenders: Extensions above/below baseline
All these proportions maintain their relationships regardless of point size, so a typeface designed with good proportions at 12 pt will remain readable at 8 pt or 72 pt.
5. Publishing and Book Design
Book Industry Standards:
- Fiction novels: 10-12 pt body text, typically Garamond, Baskerville, or Caslon
- Textbooks: 10-11 pt body, 8-9 pt captions/sidebars
- Children's books: 14-18 pt for early readers, larger for picture books
- Academic journals: 10-11 pt Times New Roman or similar serif fonts
Line Spacing (Leading): Traditionally measured in points: 10 pt text with 12 pt leading (written "10/12" and pronounced "ten on twelve") means 10 pt font with 2 pts of extra space between lines.
6. Screen Display and User Interface Design
Operating System Defaults:
- Windows: 96 DPI screen resolution → 12 pt = 16 pixels
- macOS (historical): 72 DPI → 12 pt = 12 pixels (now uses points independently of DPI)
- Retina/HiDPI displays: Points now represent logical pixels rather than physical pixels
Mobile App Guidelines:
- iOS: Uses point as device-independent unit; 1 pt = 1 logical pixel (2-3 physical pixels on Retina)
- Android: Uses density-independent pixels (dp), roughly equivalent to points
Accessibility Standards:
- WCAG 2.1: Recommends minimum 14 pt (18.67 px at 96 DPI) for body text
- Large print: 18 pt or larger considered "large print" for accessibility
7. Technical Drawing and CAD (Limited Use)
While engineering drawings typically use millimeters or inches, annotation text in CAD software (AutoCAD, SolidWorks) is specified in points:
- Drawing notes: 10-12 pt
- Dimension labels: 8-10 pt
- Title blocks: 14-24 pt
This ensures text remains readable when drawings are printed or exported to PDF.
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 Point (Typography) (pt)
How many points are in an inch?
Exactly 72 points (pt) = 1 inch (in) in the modern DTP point system used by all contemporary software. This creates simple conversions:
- 36 pt = 0.5 inches (half inch)
- 18 pt = 0.25 inches (quarter inch)
- 144 pt = 2 inches
Historically, European Didot points (≈67.55 per inch) and American pica points (≈72.27 per inch) used slightly different ratios, but these are obsolete in modern typography.
What is the difference between a point and a pixel?
Points are physical length units (1/72 inch), used for print and when physical size matters. Pixels are device-dependent digital display units whose physical size varies by screen resolution:
- On 96 DPI screens (Windows/web standard): 1 pt = 1.333 pixels
- On 72 DPI screens (old Mac standard): 1 pt = 1 pixel
- On Retina/HiDPI displays: 1 pt = 2-4 physical pixels (but still 1.333 "logical" pixels)
Use points for print design where physical dimensions matter. Use pixels or ems for responsive web design where consistency across devices matters more than absolute size.
What does 12 pt font mean?
12 pt font means the font's em square (the invisible bounding box containing the letters plus spacing) is 12 points (1/6 inch or 4.23 mm) tall. This includes:
- Ascenders: Parts above the baseline (tops of 'h', 'b', 'd')
- Descenders: Parts below the baseline (tails of 'g', 'y', 'p')
- Built-in spacing: Extra vertical room above and below
The actual visible letter height (called x-height for lowercase or cap height for capitals) is typically 60-70% of the point size. So 12 pt text has capital letters around 8-9 points (0.11-0.125 inches) tall, with the remaining space used for descenders and line spacing.
Why are there exactly 72 points in an inch?
Adobe Systems chose 72 because it's highly divisible: 72 = 2³ × 3² = 8 × 9, with factors including 2, 3, 4, 6, 8, 9, 12, 18, 24, 36. This makes common fractions simple:
- 1/2 inch = 36 pt
- 1/3 inch = 24 pt
- 1/4 inch = 18 pt
- 1/6 inch = 12 pt (standard body text)
- 1/8 inch = 9 pt
Additionally, early Macintosh screens used 72 DPI (dots per inch), making 1 point = 1 pixel—perfect for WYSIWYG ("what you see is what you get") design. Text appeared onscreen at its exact printed size.
Historically, Pierre Simon Fournier's 1737 system also used 72 points/inch for the same mathematical convenience, though his "inch" was the French royal inch, slightly different from today's international inch.
What's the difference between points and picas?
Points and picas are related typographic units:
- 1 pica = 12 points
- 6 picas = 72 points = 1 inch
- 1 pica = 1/6 inch ≈ 4.233 mm
Points are used for font sizes and small measurements (12 pt text, 2 pt line thickness). Picas are used for larger layout dimensions (column widths, page margins, grid spacing).
Example: A newspaper column might be "12 picas wide" (2 inches / 144 points) with "9 pt body text" and "1 pica margins" (12 points / 1/6 inch).
Both units are part of the same measurement system and convert simply (multiply or divide by 12), making calculations easy while providing appropriately-scaled units for different design elements.
How do I convert points to millimeters?
Formula: millimeters = points × 0.352777... (exact value: 25.4 / 72)
Simplified: millimeters ≈ points × 0.353 (accurate within 0.01%)
Quick conversions:
- 10 pt = 3.53 mm
- 12 pt = 4.23 mm
- 14 pt = 4.94 mm
- 18 pt = 6.35 mm
- 24 pt = 8.47 mm
- 72 pt = 25.4 mm (exactly 1 inch)
Reverse conversion (millimeters to points): points = millimeters × 2.834645... ≈ millimeters × 2.835
Example: A European specification requires "4 mm text." You need: 4 mm × 2.835 ≈ 11.34 pt (round to 11 pt or 11.5 pt).
Is 12 pt the same size in Word and Photoshop?
Yes, exactly. All modern software—Microsoft Word, Adobe Photoshop, InDesign, Illustrator, Google Docs, Apple Pages—uses the same DTP point definition (1/72 inch). 12 pt text will measure exactly 1/6 inch (4.23 mm) when printed from any of these applications.
However, onscreen appearance may differ slightly due to:
- Font rendering differences: Windows ClearType vs. Mac font smoothing displays the same physical size slightly differently
- Screen zoom levels: If Word is zoomed to 150%, text appears larger on screen but still prints at correct physical size
- Different default fonts: Word's default Calibri looks different from Photoshop's default Arial, even at the same point size
But when measured with a ruler on printed output, 12 pt is always exactly 1/6 inch across all applications.
Why doesn't my 12 pt text look 12 points tall on screen?
Your screen zoom level affects apparent size, but the text will still print at correct physical dimensions:
- 100% zoom: 12 pt text appears at approximately true physical size (depending on monitor size and resolution)
- 200% zoom: 12 pt text appears twice as large on screen but still prints at 1/6 inch (4.23 mm)
- 50% zoom: Text appears half-size on screen but prints correctly
Most word processors and design software show the current zoom level in the bottom toolbar. Page view at 100% zoom usually displays content close to actual print size, though this depends on your monitor's physical dimensions and resolution.
To verify true size, print a test page and measure with a ruler: 12 pt text should measure exactly 0.167 inches or 4.23 mm from the top of the tallest letter to the bottom of descenders.
What's the best point size for body text?
10-12 pt is the standard range for printed body text, with specific recommendations depending on context:
Printed Documents:
- 10 pt: Acceptable minimum; used for dense content (textbooks, references)
- 11 pt: Comfortable reading size for most book typography
- 12 pt: Default in Microsoft Word; universally acceptable for any document
Digital/Screen Display:
- 12-16 pt (or 16-21 pixels at 96 DPI): More comfortable for extended screen reading due to backlit display eye strain
- 14-18 pt: Recommended for accessibility and readers with vision impairments
Factors affecting choice:
- Font design: Fonts with larger x-height (like Verdana) are readable at smaller sizes than fonts with small x-height (like Garamond)
- Line length: Longer lines benefit from larger text (12+ pt)
- Reader age: Older audiences benefit from 12-14 pt minimum
- Reading distance: Presentations and signage require much larger text (18+ pt)
When in doubt, 12 pt is the safe, professional standard for nearly all applications.
Can I use points for web design?
Yes, but it's discouraged for screen-only designs. Here's why:
Points in CSS:
CSS supports the pt unit (1/72 inch), but it's primarily useful for print stylesheets:
@media print {
body { font-size: 11pt; } /* Predictable printed size */
h1 { font-size: 18pt; }
}
Why not for screen:
- Not responsive: Points are absolute units, don't scale with user preferences or viewport size
- Accessibility issues: Users who increase browser font size won't affect point-sized text
- Device variations: Different pixel densities make points appear inconsistent across devices
Better alternatives for screen:
- Relative units (
em,rem): Scale with user preferences - Pixels (
px): Precise control with media queries - Viewport units (
vw,vh): Scale with screen size
Best practice: Use pixels or rems for screen, points for print stylesheets.
What is leading and how does it relate to points?
Leading (pronounced "led-ing") is the vertical space between lines of text, measured in points from baseline to baseline. The term comes from traditional typesetting, where thin strips of lead metal were inserted between lines of type.
Standard leading conventions:
- Solid leading: Leading = font size (10 pt text with 10 pt leading = "10/10")
- Lines touch; rarely used except for display type
- Normal leading: Leading = 120% of font size (10 pt text with 12 pt leading = "10/12")
- Default in most word processors
- Comfortable reading with adequate space
- Loose leading: Leading = 140-160% of font size (10 pt text with 14-16 pt leading = "10/14" or "10/16")
- Airy, easy to read
- Used for accessibility, children's books
Example: 12 pt text with 14.4 pt leading means:
- Font size: 12 points (1/6 inch)
- Space from baseline to baseline: 14.4 points (0.2 inches)
- Extra space between lines: 2.4 points (0.033 inches)
Too-tight leading makes text hard to read (lines blur together). Too-loose leading creates disconnected "rivers" of white space.
Do fonts actually differ in "12 pt" size?
Yes and no. All 12 pt fonts have the same em square (the bounding box), but they can look very different sizes due to:
X-height variation:
- High x-height fonts (Verdana, Arial): Lowercase letters occupy 50-60% of em square → appear larger
- Low x-height fonts (Garamond, Bodoni): Lowercase letters occupy 40-50% of em square → appear smaller
Example:
- 12 pt Verdana: Lowercase 'x' is about 6-7 points tall (very readable)
- 12 pt Garamond: Lowercase 'x' is about 5-6 points tall (more elegant but smaller)
Both fonts have the same 12 pt em square, but Verdana allocates more of that space to letter height and less to descenders/ascenders, making it appear larger.
Practical implication: When switching fonts in a document, you may need to adjust point size to maintain similar apparent size. Replacing 12 pt Garamond with 12 pt Verdana might look too large; 11 pt Verdana may better match the original appearance.
This is why typographers often specify fonts and sizes together: "11 pt Garamond" and "10 pt Verdana" can provide similar readability despite different nominal sizes.
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: Point (Typography) to Mil/Thou
| Point (Typography) (pt) | Mil/Thou (mil) |
|---|---|
| 0.5 | 6.944 |
| 1 | 13.889 |
| 1.5 | 20.833 |
| 2 | 27.778 |
| 5 | 69.445 |
| 10 | 138.889 |
| 25 | 347.222 |
| 50 | 694.445 |
| 100 | 1,388.89 |
| 250 | 3,472.224 |
| 500 | 6,944.449 |
| 1,000 | 13,888.898 |
People Also Ask
How do I convert Point (Typography) to Mil/Thou?
To convert Point (Typography) to Mil/Thou, enter the value in Point (Typography) 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 Point (Typography) to Mil/Thou?
The conversion factor depends on the specific relationship between Point (Typography) 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 Point (Typography)?
Yes! You can easily convert Mil/Thou back to Point (Typography) by using the swap button (⇌) in the calculator above, or by visiting our Mil/Thou to Point (Typography) converter page. You can also explore other length conversions on our category page.
Learn more →What are common uses for Point (Typography) and Mil/Thou?
Point (Typography) 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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🔢 Conversion Formulas
Essential formulas for length and other conversions.
⚖️ Metric vs Imperial
Understand the differences between measurement systems.
⚠️ Common Mistakes
Learn about frequent errors and how to avoid them.
All Length Conversions
Other Length Units and Conversions
Explore other length units and their conversion options:
- Meter (m) • Point (Typography) to Meter
- Kilometer (km) • Point (Typography) to Kilometer
- Hectometer (hm) • Point (Typography) to Hectometer
- Decimeter (dm) • Point (Typography) to Decimeter
- Centimeter (cm) • Point (Typography) to Centimeter
- Millimeter (mm) • Point (Typography) to Millimeter
- Inch (in) • Point (Typography) to Inch
- Foot (ft) • Point (Typography) to Foot
- Yard (yd) • Point (Typography) to Yard
- Mile (mi) • Point (Typography) 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