Microgram to Slug Converter
Convert micrograms to slugs with our free online weight converter.
Quick Answer
1 Microgram = 6.852178e-11 slugs
Formula: Microgram × conversion factor = Slug
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.
Microgram to Slug Calculator
How to Use the Microgram to Slug Calculator:
- Enter the value you want to convert in the 'From' field (Microgram).
- The converted value in Slug will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Weight category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Microgram to Slug: Step-by-Step Guide
Converting Microgram to Slug involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Microgram = 6.85218e-11 slugsExample Calculation:
Convert 5 micrograms: 5 × 6.85218e-11 = 3.42609e-10 slugs
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 Weight conversions →What is a Microgram and a Slug?
A microgram (symbol: µg or mcg) is a unit of mass in the metric system equal to one millionth (1/1,000,000) of a gram, or one thousandth (1/1,000) of a milligram.
Key relationships:
- 1 microgram = 0.000001 grams (g)
- 1 microgram = 0.001 milligrams (mg)
- 1,000 micrograms = 1 milligram
- 1,000,000 micrograms = 1 gram
- 1 microgram ≈ 0.0000000353 ounces
Symbol variations:
- µg: Standard scientific symbol (µ = Greek letter mu)
- mcg: Common in medicine/pharmacy (avoids confusion if µ looks like m)
- Both mean exactly the same thing
The prefix "micro-":
- From Greek "mikrós" meaning "small"
- SI prefix denoting 10⁻⁶ (one millionth)
- Also used in: micrometer (µm), microsecond (µs), microliter (µL)
In perspective (how small is it?):
- 1 grain of table salt ≈ 1,000 µg (1 mg)
- 1 speck of dust ≈ 1-10 µg
- Human red blood cell ≈ 100 µg
- A typical dose of Vitamin B12 ≈ 2.4 µg
⚠️ CRITICAL SAFETY WARNING: Never confuse µg (microgram) with mg (milligram). Taking 1 mg when prescribed 1 µg = 1,000x overdose! Always double-check labels and prescriptions.
What Is a Slug?
The slug (symbol: sl or slug) is a unit of mass in the Foot-Pound-Second (FPS) system of imperial units. It is defined through Newton's second law of motion (F = ma):
1 slug = 1 lbf / (1 ft/s²)
In words: one slug is the mass that accelerates at one foot per second squared when a force of one pound-force is applied to it.
Exact Value
1 slug = 32.17404855... pounds-mass (lbm) ≈ 32.174 lbm
1 slug = 14.593902937206... kilograms ≈ 14.5939 kg
These values derive from the standard acceleration due to gravity: g = 32.174 ft/s² = 9.80665 m/s².
The Pound Confusion
The imperial system has a fundamental ambiguity: the word "pound" means two different things:
Pound-mass (lbm):
- A unit of mass (quantity of matter)
- An object has the same pound-mass everywhere in the universe
- Symbol: lbm
Pound-force (lbf):
- A unit of force (weight)
- The force exerted by one pound-mass under standard Earth gravity
- Symbol: lbf
- 1 lbf = 1 lbm × 32.174 ft/s² (weight = mass × gravity)
This creates confusion because in everyday language, "pound" can mean either, depending on context. The slug eliminates this ambiguity by serving as an unambiguous mass unit compatible with pound-force.
Why the Slug Matters: Making F = ma Work
Newton's second law: F = ma (Force = mass × acceleration)
Problem with pounds-mass and pounds-force: If you use lbm for mass and lbf for force, Newton's law becomes: F = ma / g_c
where g_c = 32.174 lbm·ft/(lbf·s²) is a dimensional conversion constant—ugly and error-prone!
Solution with slugs: Using slugs for mass and lbf for force, Newton's law works cleanly: F = ma (no extra constants needed!)
Example:
- Force: 10 lbf
- Acceleration: 5 ft/s²
- Mass: F/a = 10 lbf / 5 ft/s² = 2 slugs
- (Or in lbm: mass = 2 slugs × 32.174 = 64.348 lbm)
FPS System
The slug is part of the Foot-Pound-Second (FPS) system, also called the British Gravitational System or English Engineering System:
- Length: foot (ft)
- Force: pound-force (lbf)
- Time: second (s)
- Mass: slug (sl)
- Acceleration: feet per second squared (ft/s²)
This contrasts with the SI system (meter, kilogram, second, newton) and the pound-mass system (foot, pound-mass, second, poundal).
Note: The Microgram is part of the metric (SI) system, primarily used globally in science and trade. The Slug belongs to the imperial/US customary system.
History of the Microgram and Slug
-
Metric System Origins: The microgram is derived from the gram, a base unit in the early metric system defined in the late 18th century during the French Revolution (1790s).
-
Prefix Development: The prefix "micro-" (symbol: µ) was formalized in the late 19th century as part of the systematic development of metric prefixes to indicate a factor of 10⁻⁶ (one millionth).
-
Scientific Need: As analytical chemistry and biology advanced in the 19th and early 20th centuries, scientists needed to measure increasingly smaller masses - leading to widespread adoption of the microgram.
-
Pharmaceutical Revolution: The microgram became critically important in the 20th century with:
- Development of potent hormones (thyroid, insulin)
- Discovery of vitamins requiring trace amounts
- Creation of modern pharmaceuticals with precise dosing
- Antibiotics and specialized medications
-
Vitamin Discovery Era (1910s-1940s):
- Scientists discovered vitamins needed in microgram quantities
- Vitamin B12, biotin, folate measured in µg
- Nutrition labels began using micrograms
- Public health campaigns addressed micronutrient deficiencies
-
Symbol Standardization:
- µg adopted as standard scientific notation
- mcg introduced in medical settings to prevent confusion (µ can look like m if handwritten poorly)
- Both symbols officially recognized and equivalent
-
Modern Usage: Today, micrograms are essential in:
- Pharmaceutical dosing (especially endocrinology)
- Nutritional labeling (vitamins, minerals)
- Environmental monitoring (air/water quality)
- Toxicology and forensic science
- Analytical chemistry (trace analysis)
The Imperial Weight-Mass Problem (Pre-1900)
Before the slug was invented, the imperial system created confusion between weight (force due to gravity) and mass (quantity of matter):
Common usage: "Pound" meant weight (what a scale measures on Earth)
- "This weighs 10 pounds" meant 10 pounds-force (10 lbf)
Scientific usage: "Pound" could mean mass (quantity of matter)
- "This has 10 pounds of mass" meant 10 pounds-mass (10 lbm)
The problem: Newton's laws of motion require distinguishing force from mass. Using "pound" for both led to:
- Confusion in physics calculations
- Need for awkward gravitational conversion constants
- Errors in engineering (mixing lbf and lbm)
Arthur Mason Worthington (1852-1916)
Arthur Mason Worthington was a British physicist and professor at the Royal Naval College, Greenwich, known for his pioneering work in:
- High-speed photography of liquid drops and splashes
- Physics education and textbook writing
- Developing clearer terminology for imperial units
Around 1900, Worthington recognized that the imperial system needed a mass unit analogous to the kilogram—a unit that would make Newton's second law (F = ma) work without conversion factors.
The Slug's Introduction (c. 1900-1920)
Worthington proposed the slug as a solution:
The name: "Slug" evokes sluggishness—the tendency of massive objects to resist acceleration (inertia). A more massive object is more "sluggish" in responding to forces.
The definition: 1 slug = mass that accelerates at 1 ft/s² under 1 lbf
The relationship: 1 slug = 32.174 lbm (approximately)
This ratio (32.174) is not arbitrary—it equals the standard acceleration due to gravity in ft/s² (g = 32.174 ft/s²). This means:
- On Earth's surface, a 1-slug mass weighs 32.174 lbf
- On Earth's surface, a 1-lbm mass weighs 1 lbf
Adoption in Engineering Education (1920s-1940s)
The slug gained acceptance in American and British engineering textbooks during the early 20th century:
Advantages recognized:
- Simplified dynamics calculations (F = ma without g_c)
- Clearer distinction between force and mass
- Consistency with scientific notation (separating weight from mass)
Textbook adoption: Engineering mechanics books by authors like Beer & Johnston, Meriam & Kraige, and Hibbeler introduced the slug to generations of engineering students
University courses: American aerospace and mechanical engineering programs taught dynamics using the FPS system with slugs
Aerospace Era Embrace (1940s-1970s)
The slug became essential in American aerospace during the mid-20th century:
NACA/NASA adoption (1940s-1970s):
- Aircraft performance calculations used slugs for mass
- Rocket dynamics required precise force-mass-acceleration relationships
- Apollo program documentation used slugs extensively
Military ballistics:
- Artillery trajectory calculations
- Rocket and missile design
- Aircraft carrier catapult systems
Engineering standards:
- ASME and SAE specifications sometimes used slugs
- Aerospace contractor documentation (Boeing, Lockheed, etc.)
Decline with Metrication (1960s-Present)
Despite its technical superiority, the slug declined for several reasons:
International metrication (1960s onward):
- Most countries adopted SI units (kilogram for mass, newton for force)
- International aerospace and scientific collaboration required metric
- Slug never gained traction outside English-speaking countries
Everyday unfamiliarity:
- People use pounds (lbm/lbf) in daily life, not slugs
- No one says "I weigh 5 slugs" (they say "160 pounds")
- Slug remained a technical unit, never entering popular vocabulary
Educational shifts:
- Even American universities increasingly teach SI units first
- Engineering courses present slugs as "alternative" or "legacy" units
Software standardization:
- Modern engineering software defaults to SI (kg, N, m)
- Maintaining slug support became maintenance burden
Where Slugs Survive Today
The slug persists in specific technical niches:
American aerospace engineering:
- Aircraft weight and balance calculations (sometimes)
- Rocket propulsion dynamics
- Legacy documentation from NASA programs
Mechanical engineering dynamics courses:
- Teaching Newton's laws in FPS units
- Demonstrating unit system consistency
Ballistics and defense:
- Military projectile calculations
- Explosive dynamics
Historical technical documentation:
- 20th-century engineering reports and specifications
- Understanding legacy systems and equipment
Common Uses and Applications: micrograms vs slugs
Explore the typical applications for both Microgram (metric) and Slug (imperial/US) to understand their common contexts.
Common Uses for micrograms
The microgram is essential for measuring extremely small quantities across multiple fields:
Medicine & Pharmaceuticals
Measuring dosages of potent medications and hormones where milligrams would be too large a unit. Critical for endocrinology, psychiatry, and specialized therapeutics.
Why micrograms matter:
- Potent drugs have narrow therapeutic windows
- Prevents overdose from rounding errors
- Allows fine-tuning of hormone replacement
- Essential for pediatric dosing
Common medications in µg:
- Thyroid hormones (25-200 µg)
- Birth control (15-35 µg estrogen)
- Vitamin B12 supplements (100-1,000 µg)
- Folic acid (400-800 µg)
- Digoxin (62.5-250 µg)
⚠️ Safety: Pharmacists use mcg (not µg) on prescriptions to prevent µ being misread as m.
Convert medication doses: µg to mg | mg to µg
Nutrition
Specifying amounts of trace minerals and vitamins in food, especially those needed in very small quantities but essential for health.
Nutrients measured in µg:
- Vitamin B12 (2.4 µg/day)
- Vitamin D (10-20 µg/day)
- Vitamin K (90-120 µg/day)
- Folate (400 µg/day)
- Selenium (55 µg/day)
- Biotin (30 µg/day)
Why µg for nutrition:
- Daily requirements are very small
- Prevents decimal errors (easier than 0.0024 g)
- International standard for supplement labeling
- Matches medical terminology
Food Fortification:
- Breakfast cereals: Fortified with µg amounts of B vitamins
- Milk: Vitamin D added in µg
- Salt: Iodine fortification (45-100 µg per gram of salt)
Chemistry & Biology
Quantifying trace amounts of substances in experiments, especially in analytical chemistry, biochemistry, and molecular biology.
Laboratory Applications:
- Sample preparation: Weighing µg of rare compounds
- Protein quantification: Bradford/BCA assays use µg protein
- DNA/RNA: Quantified in µg for PCR, sequencing
- HPLC/GC: Injection standards in µg amounts
- Mass spectrometry: Detection at µg to pg levels
Biochemical Standards:
- Enzyme activity: Units per µg protein
- Cell culture: Growth factors at 1-100 µg/mL
- Antibody concentration: Often µg/mL
Environmental Science
Measuring concentrations of pollutants or contaminants in air, water, and soil at parts-per-million (ppm) or parts-per-billion (ppb) levels.
Environmental Monitoring:
-
Air quality: µg/m³ (micrograms per cubic meter)
- PM2.5 particulates
- Heavy metals (lead, mercury)
- Volatile organic compounds (VOCs)
-
Water quality: µg/L (micrograms per liter = ppb)
- Arsenic, lead, mercury in drinking water
- Pesticide residues
- Pharmaceutical contaminants
- Microplastics
-
Soil contamination: µg/kg (micrograms per kilogram = ppb)
- Heavy metal contamination
- Persistent organic pollutants
Regulatory Standards:
- EPA sets limits in µg/m³ or µg/L
- WHO guidelines use µg measurements
- EU environmental regulations
Toxicology and Forensics
Measuring extremely small amounts of toxic substances, drugs, or poisons in biological samples.
Forensic Toxicology:
- Blood drug levels (µg/L)
- Urine drug screening (µg/mL)
- Hair analysis (µg/mg hair)
- Tissue samples (µg/g tissue)
Clinical Toxicology:
- Heavy metal poisoning (blood lead: µg/dL)
- Drug overdose assessment
- Therapeutic drug monitoring
- Poison detection
Detection Limits:
- Modern instruments: Can detect picograms (0.001 µg)
- High sensitivity needed for trace toxins
Research and Development
Pharmaceutical R&D, materials science, and nanotechnology use micrograms for:
- Drug formulation studies
- Nanoparticle synthesis
- Catalyst development
- Biosensor fabrication
- Quality control testing
Use our weight converter for scientific conversions.
When to Use slugs
1. Aerospace Engineering and Aircraft Dynamics
Aerospace engineers use slugs when working in imperial units for aircraft and spacecraft calculations:
Aircraft weight and balance:
- Empty weight: 100,000 lbs = 3,108 slugs
- Loaded weight: 175,000 lbs = 5,440 slugs
- Center of gravity calculations using slugs for mass distribution
Rocket dynamics (Newton's F = ma):
- Thrust: 750,000 lbf
- Mass: 50,000 slugs (initial), decreasing as fuel burns
- Acceleration: F/m = 750,000 lbf / 50,000 slugs = 15 ft/s²
Orbital mechanics:
- Satellite mass in slugs
- Thrust-to-weight calculations
- Momentum and angular momentum in slug·ft/s units
2. Mechanical Engineering Dynamics
Engineering students and professionals analyze motion using slugs:
Newton's second law problems:
- Force: 50 lbf
- Acceleration: 10 ft/s²
- Mass: F/a = 50/10 = 5 slugs (no gravitational constant needed!)
Momentum calculations (p = mv):
- Car mass: 77.7 slugs (2,500 lbs)
- Velocity: 60 ft/s
- Momentum: p = 77.7 × 60 = 4,662 slug·ft/s
Rotational dynamics (moment of inertia):
- I = mr² (with mass in slugs, radius in feet)
- Flywheel: mass = 10 slugs, radius = 2 ft
- I = 10 × 2² = 40 slug·ft²
3. Ballistics and Projectile Motion
Military and firearms engineers use slugs for projectile calculations:
Artillery shell trajectory:
- Shell mass: 0.932 slugs (30 lbs)
- Muzzle force: 50,000 lbf
- Acceleration: a = F/m = 50,000/0.932 = 53,648 ft/s²
Bullet dynamics:
- Bullet mass: 0.000466 slug (150 grains = 0.0214 lbm)
- Chamber pressure force: 0.5 lbf (approximate average)
- Barrel acceleration calculation
Recoil analysis:
- Conservation of momentum (m_gun × v_gun = m_bullet × v_bullet)
- Gun mass: 6.22 slugs (200 lbs)
- Calculating recoil velocity in ft/s
4. Physics Education and Problem Sets
High school and college physics courses teaching imperial units:
Demonstrating unit consistency:
- Showing that F = ma works directly with slugs
- Contrasting with the g_c requirement when using lbm
Inclined plane problems:
- Block mass: 2 slugs
- Angle: 30°
- Friction force calculations in lbf
Atwood machine:
- Two masses in slugs
- Pulley system acceleration
- Tension forces in lbf
5. Automotive Engineering
Vehicle dynamics calculations using imperial units:
Braking force analysis:
- Car mass: 93.2 slugs (3,000 lbs)
- Deceleration: 20 ft/s² (emergency braking)
- Required braking force: F = ma = 93.2 × 20 = 1,864 lbf
Acceleration performance:
- Engine force (at wheels): 3,000 lbf
- Car mass: 77.7 slugs (2,500 lbs)
- Acceleration: a = F/m = 3,000/77.7 = 38.6 ft/s²
Suspension design:
- Spring force (F = kx) in lbf
- Sprung mass in slugs
- Natural frequency calculations
6. Structural Dynamics and Vibration
Engineers analyzing oscillating systems in imperial units:
Simple harmonic motion:
- F = -kx (Hooke's law, force in lbf)
- m = mass in slugs
- Natural frequency: ω = √(k/m) where m is in slugs
Seismic analysis:
- Building mass: distributed load in slugs per floor
- Earthquake force (F = ma) with acceleration in ft/s²
Mechanical vibrations:
- Damping force proportional to velocity
- Mass-spring-damper systems with m in slugs
7. Fluid Dynamics and Hydraulics
Flow and pressure calculations when using imperial units:
Momentum of flowing fluid:
- Mass flow rate: ṁ = ρAv (density in slug/ft³, area in ft², velocity in ft/s)
- Force on pipe bend: F = ṁΔv (in lbf)
Pipe flow:
- Water density: 1.938 slug/ft³ (at 68°F)
- Pressure drop calculations
- Pump power requirements
Aerodynamic forces:
- Drag force (lbf) = ½ ρ v² A C_D
- Air density: 0.00238 slug/ft³ (sea level, standard conditions)
Additional Unit Information
About Microgram (µg)
How many micrograms are in a milligram?
There are 1,000 micrograms (µg) in 1 milligram (mg).
Conversion:
- 1 mg = 1,000 µg
- To convert mg to µg: multiply by 1,000
- To convert µg to mg: divide by 1,000
Examples:
- 0.5 mg = 500 µg
- 1.5 mg = 1,500 µg
- 0.025 mg = 25 µg
- 10 mg = 10,000 µg
Memory aid: "Milli" is bigger than "micro" - mg is 1,000 times larger than µg.
Use our mg to µg converter for instant conversions.
How many micrograms are in a gram?
There are 1,000,000 micrograms (µg) in 1 gram (g).
Calculation: 1 g = 1,000 mg, and 1 mg = 1,000 µg, therefore: 1 g = 1,000 × 1,000 µg = 1,000,000 µg
Conversion:
- 1 g = 1,000,000 µg
- To convert g to µg: multiply by 1,000,000
- To convert µg to g: divide by 1,000,000
Examples:
- 0.001 g = 1,000 µg
- 0.01 g = 10,000 µg
- 0.1 g = 100,000 µg
- 1 g = 1,000,000 µg
Perspective: A grain of salt (~1 mg) contains ~1,000 µg.
What is the symbol for microgram?
The standard symbol is µg (using the Greek letter µ, pronounced "mu").
Alternative symbol: mcg (used especially in medical contexts)
Why two symbols?:
- µg: Standard scientific notation, internationally recognized
- mcg: Safer in medical prescriptions - prevents µ being misread as m
- Both mean exactly the same thing: 1 µg = 1 mcg
Safety issue:
- Handwritten µ can look like m
- "µg" misread as "mg" = 1,000x dosing error
- Medical professionals prefer "mcg" to prevent fatal errors
How to type µ:
- Mac: Option + M
- Windows: Alt + 230
- Or just type "mcg" in medical contexts
Is µg the same as mcg?
Yes! µg and mcg mean exactly the same thing.
- µg: Microgram (using Greek letter µ)
- mcg: Microgram (using letters m-c-g)
- Both = 0.001 mg = 0.000001 g
Why both exist?:
- µg: Standard in science, chemistry, environmental science
- mcg: Preferred in medicine/pharmacy for safety
- Prevents µ being misread as m (which would be mg)
Where you'll see each:
- µg: Scientific papers, environmental reports, lab results
- mcg: Prescription bottles, medical records, pharmacy labels
- Both: Nutrition labels (may show either or both)
Important: Always verify which unit - never assume!
How much is 1 microgram visually?
1 microgram is EXTREMELY small - too small to see with the naked eye.
Visual comparisons:
- 1,000 µg = 1 mg = 1 grain of table salt
- 100 µg = Approximate weight of a human red blood cell
- 10 µg = Large grain of pollen
- 1 µg = Small speck of dust
Perspective:
- 1 paperclip ≈ 1,000,000 µg (1 gram)
- 1 grain of salt ≈ 1,000 µg (1 mg)
- 1 eyelash ≈ 10-100 µg
- 1 human hair (1 cm) ≈ 60-90 µg
For medication:
- A typical Vitamin B12 tablet (1,000 µg) looks like any small pill
- The active ingredient weighs 1 mg
- The rest is filler/binder
You cannot "see" individual micrograms - you need a precision scale to measure them accurately.
What medications are dosed in micrograms?
Many potent medications use microgram dosing:
Thyroid Hormones (most common):
- Levothyroxine: 25-200 µg
- Liothyronine: 5-50 µg
Hormonal Medications:
- Birth control pills: 15-35 µg estrogen
- Testosterone: Some formulations
Cardiovascular:
- Digoxin: 62.5-250 µg
- Clonidine: 100-600 µg
Pain Management:
- Fentanyl: Patches deliver µg/hour
- (Fentanyl is EXTREMELY potent - µg doses)
Vitamins (technically supplements):
- Vitamin B12: 100-5,000 µg
- Vitamin D: 10-125 µg (400-5,000 IU)
- Folate: 400-800 µg
- Biotin: 30-10,000 µg
Why micrograms?:
- Very potent drugs need small doses
- Narrow therapeutic window
- Prevents overdose from measurement errors
⚠️ Safety: These medications have microgram-level dosing precisely because they're potent. Never adjust dose without medical supervision.
How do I measure micrograms at home?
Short answer: You generally CAN'T and SHOULDN'T measure micrograms at home.
Why not?:
- Kitchen scales: Accurate to 1 gram (1,000,000 µg) - NOT precise enough
- Jewelry scales: Accurate to 0.01-0.1 g (10,000-100,000 µg) - still not precise
- Milligram scales: Accurate to 1 mg (1,000 µg) - closer but not µg-level
- Microgram precision: Requires laboratory analytical balance ($1,000-$10,000)
For Medications:
- ✅ Use pre-measured tablets/capsules - safest option
- ✅ Follow prescription exactly - don't compound at home
- ✅ Liquid medications: Use provided dropper/syringe
- ❌ Never try to measure powder medications at home
For Supplements:
- Buy pre-dosed pills (e.g., 1,000 µg B12 tablets)
- Use products with certified dosing
- Don't buy raw powder unless you're a lab
If you need microgram precision:
- Laboratory analytical balance required
- Calibrated weights for accuracy
- Controlled environment (no air currents)
- Cost: $1,000+ for quality balance
Safety warning: ⚠️ For medications, NEVER attempt home measurement. Fatal dosing errors possible. Always use professionally prepared medications.
What's the difference between µg/mL and mg/L?
They are exactly the same!
µg/mL = mg/L (both equal parts per million in water)
Why?:
- 1 mL = 0.001 L (or 1 L = 1,000 mL)
- 1 mg = 1,000 µg
- Therefore: 1 mg/L = 1,000 µg/1,000 mL = 1 µg/mL
Examples:
- Lead in water: 15 µg/L = 0.015 mg/L
- Drug concentration: 100 µg/mL = 100 mg/L
- Vitamin solution: 50 µg/mL = 50 mg/L
Common uses:
- µg/mL: Laboratory concentrations, drug solutions
- mg/L: Environmental standards, water quality
- Both: Used interchangeably depending on field
Parts per million (ppm):
- In water: 1 ppm = 1 mg/L = 1 µg/mL
- In air: 1 ppm is different (depends on molecular weight)
How many IU is a microgram?
It depends on which vitamin! IU (International Units) convert differently for each substance.
Vitamin D (most common):
- 1 µg = 40 IU
- 1 IU = 0.025 µg
Common Vitamin D conversions:
- 400 IU = 10 µg
- 800 IU = 20 µg
- 1,000 IU = 25 µg
- 2,000 IU = 50 µg
- 5,000 IU = 125 µg
Vitamin A (retinol):
- 1 IU ≈ 0.3 µg retinol
- 1 µg retinol ≈ 3.33 IU
Vitamin E (α-tocopherol):
- 1 IU ≈ 0.67 mg α-tocopherol
- (Note: mg not µg for Vitamin E!)
Why different?:
- IU measures biological activity, not mass
- Each vitamin has different potency
- Historical measurement system
- Modern labels often show both µg and IU
Tip: Check supplement labels - most show both µg and IU for clarity.
What is µg/dL in blood tests?
µg/dL = micrograms per deciliter - commonly used in blood test results.
What it means:
- Concentration of a substance in blood
- 1 dL = 100 mL (1 deciliter = 10th of a liter)
- µg/dL tells you: micrograms per 100 milliliters of blood
Common blood tests using µg/dL:
Blood Lead Level:
- Normal: <5 µg/dL
- Elevated: 5-10 µg/dL
- High: >10 µg/dL (concern)
- Toxic: >45 µg/dL
Blood Glucose (note: mg/dL, not µg/dL):
- Normal fasting: 70-100 mg/dL
- (This is milligrams, not micrograms!)
Iron/Ferritin: Sometimes reported in µg/dL Vitamin B12: Often ng/mL or pg/mL (nanograms/picograms)
Conversion:
- 1 µg/dL = 10 µg/L
- 1 µg/dL = 0.01 mg/L
- 1 µg/dL = 10 ng/mL
Clinical significance:
- Reference ranges vary by lab
- Always check lab's normal range
- Consult healthcare provider for interpretation
Note: µg/dL is different from µg/mL:
- 1 µg/dL = 0.01 µg/mL (100 times smaller)
About Slug (sl)
How is the slug defined?
Answer: 1 slug = 1 lbf / (1 ft/s²) — the mass that accelerates at 1 ft/s² under 1 lbf
The slug is defined through Newton's second law (F = ma):
Rearranging: m = F/a
Definition: If a force of 1 pound-force produces an acceleration of 1 foot per second squared, the mass is 1 slug.
In equation form: 1 slug = 1 lbf / (1 ft/s²)
This makes Newton's law work cleanly: F (lbf) = m (slugs) × a (ft/s²)
Alternative definition (equivalent): 1 slug = 32.174 pounds-mass (lbm)
This number (32.174) comes from standard Earth gravity: g = 32.174 ft/s²
How many pounds-mass are in a slug?
Answer: 1 slug = 32.174 pounds-mass (lbm) exactly
This relationship derives from the gravitational constant:
Standard gravity: g = 32.17405 ft/s² (exactly, by definition)
Weight-mass relationship: Weight (lbf) = Mass (lbm) × g / g_c
where g_c = 32.174 lbm·ft/(lbf·s²) (dimensional conversion constant)
On Earth: A mass of 1 lbm experiences a weight of 1 lbf Therefore: A mass of 32.174 lbm experiences a weight of 32.174 lbf
But also: A mass of 1 slug experiences a weight of 32.174 lbf (by definition)
Conclusion: 1 slug = 32.174 lbm
Example:
- Person: 160 lbm
- In slugs: 160 ÷ 32.174 = 4.97 slugs
Why is the slug unit used?
Answer: To simplify F = ma calculations in imperial units by eliminating the need for gravitational conversion constants
The problem without slugs:
Using pounds-mass (lbm) and pounds-force (lbf) in Newton's law requires:
F = ma / g_c
where g_c = 32.174 lbm·ft/(lbf·s²)
This is awkward and error-prone!
The solution with slugs:
Using slugs for mass and lbf for force, Newton's law is simple:
F = ma (no conversion constant!)
Example comparison:
Force: 100 lbf Acceleration: 5 ft/s² Mass = ?
Without slugs (using lbm): m = F × g_c / a = 100 × 32.174 / 5 = 643.48 lbm
With slugs: m = F / a = 100 / 5 = 20 slugs
Much simpler! (Though 20 slugs = 643.48 lbm, same physical mass.)
How do I convert between slugs and kilograms?
Answer: 1 slug = 14.5939 kg (multiply slugs by 14.5939 to get kg)
Slugs to kilograms: kg = slugs × 14.5939
Examples:
- 1 slug = 14.5939 kg
- 5 slugs = 5 × 14.5939 = 72.97 kg
- 10 slugs = 10 × 14.5939 = 145.94 kg
Kilograms to slugs: slugs = kg ÷ 14.5939 (or kg × 0.0685218)
Examples:
- 10 kg = 10 ÷ 14.5939 = 0.685 slugs
- 70 kg = 70 ÷ 14.5939 = 4.80 slugs
- 100 kg = 100 ÷ 14.5939 = 6.85 slugs
Quick approximation:
- 1 slug ≈ 14.6 kg
- 1 kg ≈ 0.069 slugs (roughly 1/15th slug)
Why don't people use slugs in everyday life?
Answer: Slugs are awkward for everyday masses and unfamiliar to the general public
Practical reasons:
1. Unfamiliar numbers: Converting common weights to slugs produces strange values
- "I weigh 5.6 slugs" sounds odd compared to "180 pounds"
- A gallon of milk is "0.26 slugs" vs. "8.6 pounds"
2. No tradition: Unlike pounds (used for centuries in commerce), slugs were invented for technical calculations only
3. Pounds work fine for daily life: The lbf/lbm ambiguity doesn't matter when you're just measuring weight on a scale
4. Imperial persistence: Americans use pounds because of cultural tradition, not technical correctness
Technical fields use slugs precisely because they eliminate ambiguity in force-mass calculations, but this advantage is irrelevant for grocery shopping or body weight.
Cultural reality: People will continue saying "pounds" for everyday masses, while engineers quietly use slugs behind the scenes.
What's the difference between a slug and a pound?
Answer: Slug measures mass; pound can mean either mass (lbm) or force/weight (lbf)
Slug:
- Always a unit of mass
- 1 slug = 32.174 lbm = 14.5939 kg
- Measures quantity of matter (inertia)
- Used in F = ma calculations
Pound-mass (lbm):
- Unit of mass
- 1 lbm = 1/32.174 slug = 0.453592 kg
- Quantity of matter
Pound-force (lbf):
- Unit of force (weight)
- Force exerted by 1 lbm under standard Earth gravity
- 1 lbf = force needed to accelerate 1 slug at 1 ft/s²
Relationship on Earth:
- 1 slug has a mass of 32.174 lbm
- 1 slug weighs (exerts a force of) 32.174 lbf on Earth
- 1 lbm weighs 1 lbf on Earth
Key insight: The numerical coincidence (1 lbm weighs 1 lbf on Earth) obscures the fact that mass and force are different physical quantities. Slugs eliminate this confusion.
Is the slug still used in engineering?
Answer: Yes, but rarely—mainly in American aerospace and dynamics courses
Where slugs are still used:
1. Aerospace engineering:
- NASA and aerospace contractors for some calculations
- Aircraft dynamics and performance
- Rocket propulsion when working in imperial units
2. Engineering education:
- Mechanical engineering dynamics courses
- Teaching Newton's laws with imperial units
- Demonstrating unit consistency
3. Defense/ballistics:
- Military projectile calculations
- Weapons systems analysis
4. Legacy documentation:
- Understanding 20th-century engineering reports
- Maintaining older systems specified in FPS units
Where slugs are NOT used:
- International engineering (uses kilograms)
- Daily life (people use pounds)
- Most modern engineering software (defaults to SI units)
- Scientific research (exclusively metric)
Current status: Declining but not extinct; maintained for continuity with older American engineering systems
Can I weigh myself in slugs?
Answer: Technically yes, but practically no—scales measure force (weight), not mass
The technical issue:
Bathroom scales measure weight (force in lbf or kg-force), not mass:
- They use a spring that compresses under gravitational force
- The readout is calibrated to show "pounds" or "kilograms"
Converting scale reading to slugs:
If your scale says "160 pounds" (meaning 160 lbf weight):
- Your mass = 160 lbm / 32.174 = 4.97 slugs
Or if metric scale says "70 kg" (meaning 70 kg-force weight):
- Your mass = 70 kg / 14.5939 = 4.80 slugs
Why people don't do this:
- Unfamiliar: "I weigh 5 slugs" sounds strange
- Extra math: Requires division by 32.174
- No benefit: Pounds work fine for personal weight tracking
Correct statement: "My mass is 4.97 slugs" (not "I weigh 4.97 slugs"—weight is measured in lbf!)
How does the slug relate to Newton's second law?
Answer: The slug is defined to make F = ma work directly with pounds-force and ft/s²
Newton's second law: Force = mass × acceleration
In slug system (FPS units):
- Force in pound-force (lbf)
- Mass in slugs (sl)
- Acceleration in feet per second squared (ft/s²)
Result: F (lbf) = m (slugs) × a (ft/s²)
Example:
- Mass: 2 slugs
- Acceleration: 15 ft/s²
- Force: F = 2 × 15 = 30 lbf
Why this works: The slug is defined such that 1 lbf accelerates 1 slug at 1 ft/s²
Contrast with lbm system (more complicated): F (lbf) = m (lbm) × a (ft/s²) / g_c
where g_c = 32.174 lbm·ft/(lbf·s²)
Same example using lbm:
- Mass: 2 slugs = 64.348 lbm
- Acceleration: 15 ft/s²
- Force: F = 64.348 × 15 / 32.174 = 30 lbf (same result, more complex calculation)
The slug's purpose: Eliminate the g_c conversion factor!
What does "slug" mean and where does the name come from?
Answer: "Slug" evokes sluggishness or inertia—the resistance of mass to acceleration
Etymology:
The term was coined by British physicist Arthur Mason Worthington around 1900.
The metaphor:
- Sluggish = slow to respond, resistant to movement
- Inertia = the tendency of massive objects to resist acceleration
- A more massive object is more "sluggish"
The connection to physics:
Inertial mass is the property of matter that resists acceleration:
- Larger mass → greater "sluggishness" → harder to accelerate
- Smaller mass → less "sluggish" → easier to accelerate
Example:
- Push a shopping cart (low mass) → accelerates easily (not very sluggish)
- Push a truck (high mass in slugs) → accelerates slowly (very sluggish!)
Word choice reasoning: Worthington wanted a vivid, memorable term that conveyed the physical concept of inertia while fitting the imperial system of units (slug, pound, foot).
Alternative names considered: The unit could have been called "inertia pound" or "force-pound," but "slug" was catchier and emphasized the conceptual link to resistance to motion.
Why is 1 slug equal to 32.174 pounds-mass specifically?
Answer: Because 32.174 ft/s² is the standard acceleration due to Earth's gravity (g)
The relationship derives from weight-force:
Weight (lbf) = mass (lbm) × gravity (ft/s²) / g_c
where g_c = 32.174 lbm·ft/(lbf·s²) is the dimensional conversion constant
On Earth (g = 32.174 ft/s²):
- 1 lbm weighs: 1 lbm × 32.174 / 32.174 = 1 lbf
Also by definition:
- 1 slug weighs: 1 slug × 32.174 ft/s² = 32.174 lbf (from F = ma)
Combining these:
- If 1 lbm weighs 1 lbf, and 1 slug weighs 32.174 lbf...
- Then 1 slug must equal 32.174 lbm!
The number 32.174 is Earth's standard gravitational acceleration: g = 32.17405 ft/s² ≈ 32.174 ft/s²
Consequence: The slug naturally relates to pounds-mass through Earth's gravity, even though the slug is a mass unit (not dependent on gravity).
On other planets:
- Mass is still measured in slugs (unchanged)
- Weight changes (different g value)
- Example: 1 slug on Moon weighs only 5.32 lbf (not 32.174 lbf)
Will the slug eventually disappear?
Answer: Likely yes—it's declining rapidly as engineering shifts to SI units globally
Factors driving obsolescence:
1. International standardization:
- Global engineering collaborations require common units (SI/metric)
- Slug is unknown outside U.S./British contexts
2. Educational shifts:
- Even American universities teach SI units first
- Slugs relegated to "alternative units" or historical notes
3. Software migration:
- Modern CAD/simulation software defaults to metric (kg, N, m)
- Maintaining slug support is extra development cost
4. Generational change:
- Engineers trained in FPS/slug units are retiring
- New graduates work primarily in metric
5. Daily life disconnect:
- Slug never entered common vocabulary (unlike "pound")
- No cultural attachment to preserve it
Where it might persist longest:
- Legacy aerospace systems (maintaining old aircraft/rockets)
- Specialized defense applications
- Historical engineering documentation
- Educational examples showing unit system consistency
Likely outcome: Slug will become a "historical unit" known primarily to:
- Engineering historians
- Those maintaining 20th-century equipment
- Educators explaining evolution of unit systems
Similar to how poundals (another imperial force unit) are now essentially extinct despite once being scientifically "correct."
Conversion Table: Microgram to Slug
| Microgram (µg) | Slug (sl) |
|---|---|
| 0.5 | 0 |
| 1 | 0 |
| 1.5 | 0 |
| 2 | 0 |
| 5 | 0 |
| 10 | 0 |
| 25 | 0 |
| 50 | 0 |
| 100 | 0 |
| 250 | 0 |
| 500 | 0 |
| 1,000 | 0 |
People Also Ask
How do I convert Microgram to Slug?
To convert Microgram to Slug, enter the value in Microgram in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our weight converter page to convert between other units in this category.
Learn more →What is the conversion factor from Microgram to Slug?
The conversion factor depends on the specific relationship between Microgram and Slug. 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 Slug back to Microgram?
Yes! You can easily convert Slug back to Microgram by using the swap button (⇌) in the calculator above, or by visiting our Slug to Microgram converter page. You can also explore other weight conversions on our category page.
Learn more →What are common uses for Microgram and Slug?
Microgram and Slug are both standard units used in weight measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our weight converter for more conversion options.
For more weight conversion questions, visit our FAQ page or explore our conversion guides.
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Last verified: December 3, 2025