Dram to Slug Converter
Convert drams to slugs with our free online weight converter.
Quick Answer
1 Dram = 0.000121 slugs
Formula: Dram × conversion factor = Slug
Use the calculator below for instant, accurate conversions.
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Dram to Slug Calculator
How to Use the Dram to Slug Calculator:
- Enter the value you want to convert in the 'From' field (Dram).
- 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 Dram to Slug: Step-by-Step Guide
Converting Dram to Slug involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Dram = 0.00012141 slugsExample Calculation:
Convert 5 drams: 5 × 0.00012141 = 0.00060705 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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Avoirdupois Dram (Commercial)
The avoirdupois dram is defined in the common weight system used for most goods:
Relationships:
- 1 dram = 1/16 ounce (avoirdupois)
- 1 dram = 1/256 pound (avoirdupois)
- 1 dram = 27.34375 grains (exactly)
- 1 dram ≈ 1.7718451953125 grams (exactly)
Symbol: dr, dr av, or dr avdp
Historical use: General commerce, precious materials, spices, ammunition powder charges.
Apothecary/Troy Dram (Pharmaceutical)
The apothecary dram (also called drachm) belongs to the apothecaries' weight system used historically in pharmacy:
Relationships:
- 1 dram (ʒ) = 1/8 ounce (apothecary)
- 1 dram = 3 scruples
- 1 dram = 60 grains (exactly)
- 1 dram ≈ 3.8879346 grams (exactly)
Symbol: ʒ (resembles the number 3, representing 3 scruples)
Historical use: Compounding medicines, pharmaceutical measurements, medical prescriptions.
The Critical Difference
Apothecary dram = 2.194 × Avoirdupois dram
This 2.2× ratio causes confusion. Historical recipes and medical texts must specify which system they use, or dosages could be dangerously incorrect.
Fluid Dram (Volume, Not Weight)
Adding to the confusion, the fluid dram is a unit of volume:
Fluid dram (imperial):
- 1/8 fluid ounce (imperial)
- ≈ 3.5516 mL
Fluid dram (US):
- 1/8 fluid ounce (US)
- ≈ 3.6967 mL
Symbol: fl dr, fl ʒ, or ℈
This is completely separate from weight drams, though historically related (1 fluid dram of water weighs approximately 1 avoirdupois dram).
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 Dram is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Slug belongs to the imperial/US customary system.
History of the Dram and Slug
Ancient Greek Drachma (600 BCE - 300 CE)
The drachma coin: Greek city-states minted silver coins called drachmas, weighing approximately 4.3 grams (varying by region and period).
Origin of name: "Drachma" (δραχμή) derives from "drax" (handful) or "drassomai" (to grasp), possibly referring to a handful of six obol coins.
Weight standard: The Attic drachma (Athens) weighed about 4.3 g of silver, becoming a widespread weight and monetary standard.
Roman Adoption (300 BCE - 500 CE)
Drachma in Roman medicine: Roman physicians adopted Greek medical practices, including pharmaceutical measurements based on the drachma.
Galen's formulations: The physician Galen (129-216 CE) used drachmas extensively in medicinal recipes, establishing the unit in medical tradition.
Byzantine and Islamic Medicine (500-1200 CE)
Byzantine continuation: The Eastern Roman Empire (Byzantium) preserved Greek medical texts, maintaining the drachm as a pharmaceutical unit.
Islamic Golden Age: Arab physicians (Al-Razi, Avicenna) translated Greek medical works, incorporating drachms into Arabic pharmacy. The dirham (Arabic coin) shares the same etymological root.
Transmission to Europe: Through Islamic Spain and Sicily, Arabic medical knowledge returned to Western Europe (11th-13th centuries), bringing pharmaceutical drachm measurements.
Medieval European Apothecaries (1200-1600)
Apothecary guilds: European cities established apothecary guilds, standardizing medicinal weights based on the drachm.
The apothecary system:
- 1 pound (lb ap) = 12 ounces
- 1 ounce (℥) = 8 drams (ʒ)
- 1 dram = 3 scruples (℈)
- 1 scruple = 20 grains (gr)
Result: 1 apothecary dram = 60 grains
Symbol evolution: The symbol ʒ (scribal abbreviation for Latin "drachma") became standard for the dram.
British Standardization (1600-1800)
London Pharmacopoeia (1618): The first official British pharmacopoeia standardized apothecary weights, including the dram at 60 grains.
Avoirdupois emergence: Simultaneously, the avoirdupois system developed for general commerce, creating a different dram:
- Avoirdupois dram = 1/16 ounce = 27.34375 grains
Coexistence: Two dram standards coexisted—apothecary for medicine, avoirdupois for trade.
American Adoption (1776-1900)
U.S. Pharmacopeia (1820): The first U.S. Pharmacopeia codified pharmaceutical measurements, adopting British apothecary standards including the dram.
Medical education: American medical schools taught apothecary measurements. Physicians wrote prescriptions using symbols like ʒ for drams.
Commercial use: Avoirdupois drams measured gunpowder, spices, precious materials, and other commodities.
Ammunition Application (1800s-Present)
Black powder charges: Early firearms used black powder measured in drams. A "3-dram load" meant 3 avoirdupois drams of powder.
Dram equivalent: With the transition to smokeless powder (1880s onward), manufacturers created "dram equivalent" ratings—the amount of smokeless powder producing the same velocity as a given dram measure of black powder.
Modern shotshells: Today's shotgun shells still reference "3 dram equivalent" or "3¼ dram equivalent" on the box, though actual powder weights are in grains or grams.
Metrication and Decline (1900-Present)
British pharmacy (1970): The UK officially abandoned apothecary weights, switching entirely to metric (grams, milligrams).
American pharmacy (1970s-1980s): U.S. pharmacy schools phased out apothecary measurements, adopting metric. By 1990, nearly all prescriptions used metric units.
Persistence:
- Ammunition: Dram equivalent ratings continue
- Historical recipes: Antique cookbooks and medical texts
- Collectors: Antique apothecary scales and weights
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: drams vs slugs
Explore the typical applications for both Dram (imperial/US) and Slug (imperial/US) to understand their common contexts.
Common Uses for drams
1. Ammunition and Reloading
Shotshell ratings: Manufacturers mark shotgun shells with "dram equivalent" to indicate approximate velocity/power level.
Why still used? Tradition and familiarity. Shooters understand "3 dram load" means standard power, while "3¾ dram" is heavy magnum.
Reloading manuals: Some reloading data references dram equivalents alongside modern grain measurements.
2. Historical Recipe Interpretation
19th-century cookbooks: Recipes may call for "1 dram of nutmeg" or "2 drams of ginger."
Conversion challenge: Must determine if the recipe uses avoirdupois or apothecary drams (usually avoirdupois for cooking).
Modern equivalent: 1 avoirdupois dram ≈ 1.77 grams ≈ 1/3 teaspoon (for dry spices)
3. Antique Apothecary Items
Collectible scales: Antique apothecary scales often have dram weights marked with ʒ.
Medicine bottles: Historical pharmacy bottles may indicate contents in drams.
Historical research: Understanding drams is essential for interpreting 18th-19th century medical texts.
4. Pharmaceutical History
Old pharmacopoeias: Historical pharmaceutical formulas use apothecary drams.
Example prescription (1850s): "℞ Quinine sulfate ʒij" = Take 2 drams of quinine sulfate
Modern interpretation: 2 apothecary drams = 7.78 grams
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 Dram (dr)
How many drams are in an ounce (avoirdupois)?
Exactly 16 avoirdupois drams = 1 avoirdupois ounce.
This is the definition:
- 1 oz av = 16 dr av
- 1 dr av = 1/16 oz av = 0.0625 oz
How many grams are in a dram (avoirdupois)?
1 avoirdupois dram = 1.7718451953125 grams (exactly).
Practical approximation: 1 dr av ≈ 1.77 g
Derivation: 1 pound av = 453.59237 grams (exact) 1 pound = 256 drams 1 dram = 453.59237 ÷ 256 = 1.77185 g
Is a dram a unit of mass or volume?
Both exist, which causes significant confusion:
Mass (weight):
- Avoirdupois dram (dr): 1.772 g
- Apothecary dram (ʒ): 3.888 g
Volume:
- Fluid dram (fl dr, US): 3.697 mL
- Fluid dram (fl dr, imperial): 3.552 mL
Context matters:
- Pharmacy/medicine historically: could be either (check symbols)
- General commerce: usually weight
- Modern usage: rare except ammunition (weight-related rating)
What's the difference between avoirdupois and apothecary drams?
Avoirdupois dram (commercial):
- 1/16 ounce avoirdupois
- 27.34375 grains
- 1.772 grams
- Used for general goods
Apothecary dram (pharmaceutical):
- 1/8 ounce apothecary
- 60 grains
- 3.888 grams
- Used for medicines
Key difference: Apothecary dram is 2.19× heavier than avoirdupois dram.
What does the symbol ʒ mean?
The symbol ʒ represents the apothecary dram.
Origin: Scribal abbreviation of Latin "drachma" or "dragma."
Appearance: Resembles a fancy number "3," which is appropriate since 1 dram = 3 scruples.
Usage: Historical pharmaceutical prescriptions: "℞ Morphine ʒi" = Take 1 dram of morphine
What is a dram equivalent in ammunition?
"Dram equivalent" is a velocity/power rating for shotgun shells, not actual powder weight.
Historical context: Black powder shotgun loads used actual drams of powder (e.g., "3 drams of black powder").
Modern meaning: A "3 dram equivalent" smokeless powder load produces approximately the same muzzle velocity as a historical 3-dram black powder load.
Actual powder weight: Modern "3 dram equivalent" loads typically contain 18-22 grains of smokeless powder (less than 1 actual dram by weight).
Rating scale:
- 2¾ dram eq: Light/target
- 3 dram eq: Standard
- 3¼ dram eq: Magnum
- 3¾ - 4 dram eq: Heavy magnum
Do doctors still use drams?
No, modern medicine uses metric units exclusively.
Historical use: 19th and early 20th century physicians wrote prescriptions using apothecary measurements including drams (ʒ).
Transition:
- UK: Abandoned apothecary units in 1970
- US: Phased out 1970s-1990s
Current practice: All modern prescriptions use milligrams (mg), grams (g), and milliliters (mL). Drams are historical artifacts.
How do I convert historical dram measurements?
Step 1: Identify the system
- Pharmacy/medicine: Likely apothecary dram (3.888 g)
- Cooking/commerce: Likely avoirdupois dram (1.772 g)
Step 2: Check for symbols
- ʒ symbol: Definitely apothecary
- "dr" or no symbol: Context-dependent (probably avoirdupois for cooking)
Step 3: Convert to grams
- Avoirdupois: drams × 1.772
- Apothecary: drams × 3.888
Step 4: Convert to modern measure
- Grams to teaspoons (dry ingredients): ~5 g per tsp
- Grams to milliliters (liquids): depends on density
Can I still buy dram weights?
Yes, as antique collectibles, but not for practical use.
Antique apothecary weights: Available from antique dealers, often brass or bronze, marked with ʒ symbol.
Modern equivalents: Not manufactured. Use gram scales instead.
Collectible value: Complete sets of 18th-19th century apothecary weights command $100-500+ depending on condition.
Why did pharmacy abandon drams?
Multiple reasons drove metrication:
1. International standardization: Metric system adopted globally for science and medicine.
2. Safety: Multiple dram systems (avoirdupois vs. apothecary) created dangerous confusion.
3. Ease of calculation: Decimal metric system simpler than fractional apothecary system.
4. Precision: Milligrams allow more precise dosing than grains/scruples/drams.
Result: By 1990, virtually all pharmacy worldwide used metric exclusively.
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: Dram to Slug
| Dram (dr) | Slug (sl) |
|---|---|
| 0.5 | 0 |
| 1 | 0 |
| 1.5 | 0 |
| 2 | 0 |
| 5 | 0.001 |
| 10 | 0.001 |
| 25 | 0.003 |
| 50 | 0.006 |
| 100 | 0.012 |
| 250 | 0.03 |
| 500 | 0.061 |
| 1,000 | 0.121 |
People Also Ask
How do I convert Dram to Slug?
To convert Dram to Slug, enter the value in Dram 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 Dram to Slug?
The conversion factor depends on the specific relationship between Dram 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 Dram?
Yes! You can easily convert Slug back to Dram by using the swap button (⇌) in the calculator above, or by visiting our Slug to Dram converter page. You can also explore other weight conversions on our category page.
Learn more →What are common uses for Dram and Slug?
Dram 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: February 19, 2026