Slug to Pennyweight Converter
Convert slugs to pennyweights with our free online weight converter.
Quick Answer
1 Slug = 9384.095607 pennyweights
Formula: Slug × conversion factor = Pennyweight
Use the calculator below for instant, accurate conversions.
Our Accuracy Guarantee
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.
Slug to Pennyweight Calculator
How to Use the Slug to Pennyweight Calculator:
- Enter the value you want to convert in the 'From' field (Slug).
- The converted value in Pennyweight 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 Slug to Pennyweight: Step-by-Step Guide
Converting Slug to Pennyweight involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Slug = 9384.1 pennyweightsExample Calculation:
Convert 5 slugs: 5 × 9384.1 = 46920.5 pennyweights
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.
Need to convert to other weight units?
View all Weight conversions →What is a Slug and a Pennyweight?
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).
What Is a Pennyweight?
The pennyweight (symbol: dwt) is a unit of mass within the troy weight system, equal to exactly 1.55517384 grams or 1/20th of a troy ounce. It consists of precisely 24 grains, making it a convenient intermediate unit for measuring precious metals and gemstones.
Troy vs. Avoirdupois Systems
The pennyweight belongs to the troy weight system, which differs fundamentally from the avoirdupois system used for most everyday weights:
- Troy system: 12 ounces = 1 pound (used for precious metals, gemstones)
- Avoirdupois system: 16 ounces = 1 pound (used for general commerce)
- Key difference: A troy ounce (31.1035 g) is heavier than an avoirdupois ounce (28.3495 g), but a troy pound (373.24 g) is lighter than an avoirdupois pound (453.59 g)
Official Definition
Since the 1959 international yard and pound agreement, the pennyweight is defined as:
1 dwt = 24 grains = 0.05 troy ounces = 1.55517384 grams (exact)
This definition is recognized by the United States, United Kingdom, Canada, Australia, New Zealand, and South Africa, ensuring consistency in precious metals trading worldwide.
Note: The Slug is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Pennyweight belongs to the imperial/US customary system.
History of the Slug and Pennyweight
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
Ancient Origins: The Silver Penny
The pennyweight's history traces to Anglo-Saxon England, where silver pennies served as both currency and weight standards. During the reign of King Offa of Mercia (757-796 AD), silver pennies were standardized at one pennyweight each, creating a direct relationship between monetary value and precious metal weight.
This system meant that:
- 1 silver penny = 1 pennyweight of silver
- 20 pennies = 1 shilling = 1 troy ounce of silver
- 240 pennies = 1 pound sterling = 1 troy pound of silver
This elegant correspondence between money and weight lasted nearly 1,200 years in principle, though the silver content of coins gradually decreased over centuries.
Medieval Standardization (1266-1327)
The Composition of Yards and Perches statute of 1266 under King Henry III formally standardized English weights and measures, including the pennyweight at 24 grains. This was reinforced by the Tractatus de Ponderibus et Mensuris (Treatise on Weights and Measures) issued during the reign of Edward I (1303-1307).
The Worshipful Company of Goldsmiths, granted its royal charter in 1327, became the official regulatory body for precious metals in England. The company enforced pennyweight standards through its hallmarking system, which required all gold and silver items to be assayed (tested for purity) and stamped with official marks. Goldsmiths' Hall in London became the center of this regulatory system—hence the term "hallmark."
Troyes Connection
The term "troy weight" derives from Troyes, France, a major medieval trading city hosting international fairs where merchants from across Europe gathered. By the 12th-13th centuries, Troyes had developed standardized weight systems for precious metals that were adopted by merchants throughout Europe.
English goldsmiths adopted the Troyes system because it was already used by continental traders, ensuring consistency in international precious metals commerce. The system's subdivision structure (1 pound = 12 ounces, 1 ounce = 20 pennyweights, 1 pennyweight = 24 grains) reflected medieval base-12 and base-20 counting preferences.
British Imperial Codification (1824-1878)
The British Weights and Measures Act of 1824 consolidated various troy weight standards used across Britain, officially defining the troy pound as 5,760 grains and the pennyweight as 1/240th of a troy pound (24 grains).
The Weights and Measures Act of 1878 refined these definitions and legally mandated troy weights for precious metals transactions throughout the British Empire. This act specified that gold, silver, platinum, and precious stones must be weighed using troy units, with the pennyweight serving as the practical working unit for jewelers and dealers.
American Adoption
The United States adopted the British troy system for precious metals following independence. The U.S. Coinage Act of 1792 established the dollar based on a specific weight of silver (371.25 grains = 15.4375 pennyweights), directly linking American currency to pennyweight standards.
The National Bureau of Standards (now NIST) formalized the pennyweight in U.S. regulations, and it remains a legally recognized unit for precious metals commerce under U.S. law today.
International Agreement (1959)
The 1959 international yard and pound agreement among English-speaking nations established exact metric equivalents for imperial units, defining the grain (and therefore the pennyweight) in terms of the kilogram:
- 1 grain = exactly 64.79891 milligrams
- 1 pennyweight = 24 grains = exactly 1.55517384 grams
This agreement ended minor variations in troy weight definitions across different countries and established the standard used worldwide today.
Modern Persistence
Despite metrication efforts in the United Kingdom (1965-present), Australia (1970s), and other Commonwealth nations, the pennyweight persists in the precious metals and jewelry industries. The unit's survival reflects:
- International trade standards: Precious metals are traded globally in troy ounces and pennyweights
- Industry infrastructure: Scales, reference books, and pricing systems are built around troy units
- Practical convenience: Pennyweights provide appropriate precision for jewelry work
- Legal requirements: Many jurisdictions still mandate troy weights for bullion hallmarking
The London Bullion Market Association (LBMA), established 1987, continues to use troy ounces (and by extension, pennyweights) as the global standard for precious metals trading, ensuring the unit's continued relevance.
Common Uses and Applications: slugs vs pennyweights
Explore the typical applications for both Slug (imperial/US) and Pennyweight (imperial/US) to understand their common contexts.
Common Uses for 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)
When to Use pennyweights
1. Jewelry Manufacturing and Valuation
Jewelers use pennyweights as their primary working unit for several reasons:
Precision without unwieldiness: A pennyweight provides finer precision than troy ounces (1/20th oz increments) without requiring the tiny fractions that grain measurements would demand. A jeweler can easily work with "5.5 dwt of gold" rather than "110 grains" or "0.275 troy ounces."
Pricing calculations: Precious metal dealers quote prices per pennyweight for smaller quantities. For example, if gold is $2,000/troy ounce, it's $100/dwt ($2,000 ÷ 20). This makes quick calculations easier: a 6 dwt ring contains $600 worth of gold.
Material estimation: When designing custom jewelry, goldsmiths estimate required material in pennyweights: "This ring design will need approximately 8 pennyweights of 14-karat gold, plus 2 pennyweights for the setting."
Scrap valuation: When buying or selling scrap gold/silver, dealers weigh items in pennyweights to calculate melt value: "Your broken gold chain weighs 12.3 pennyweights at 14-karat purity, which contains 7.175 dwt of pure gold."
Industry standard scales: Professional jewelers' scales typically display troy ounces subdivided into 20 pennyweights, with precision to 0.01 dwt (0.24 grains).
2. Precious Metals Trading and Refining
Refinery lot tracking: When refineries process precious metals, they track batches in troy ounces and pennyweights: "Batch #4782: 347 oz 15 dwt of sterling silver scrap."
Assay reporting: Assay offices (testing precious metal purity) report results in pennyweights: "Sample contained 18.65 dwt of pure gold and 1.35 dwt of copper alloy."
Bullion fractional trading: Small precious metals dealers use pennyweights for transactions smaller than full troy ounces: "We buy silver at $1.20/dwt" ($24/oz).
Hallmarking records: Official hallmarking offices record item weights in pennyweights when stamping fineness marks: "Ring assayed and hallmarked: 5.2 dwt, 18kt gold."
3. Gemstone Settings and Diamond Work
While gemstones themselves are weighed in carats (1 carat = 200 mg), the metal settings are measured in pennyweights:
Prong settings: "Four-prong platinum setting for 1-carat diamond: 1.8 dwt" Bezels: "18kt gold bezel for round cabochon: 2.3 dwt" Channel settings: "Platinum channel for seven 0.25ct diamonds: 4.5 dwt"
Conversion reference: 1 pennyweight = 7.776 metric carats (though carats aren't used for metal)
4. Coin Collecting (Numismatics)
Coin collectors reference pennyweights to verify authenticity and silver/gold content:
Historical silver coins: Pre-1965 U.S. dimes, quarters, and half-dollars contain 90% silver. Their pennyweight ratings help collectors calculate precious metal value:
- 1964 Kennedy half-dollar: 7.234 dwt silver content
- 1964 Washington quarter: 3.617 dwt silver content
- 1964 Roosevelt dime: 1.447 dwt silver content
Gold coins: American Gold Eagles, Krugerrands, and other bullion coins are often referenced in pennyweights for smaller transactions:
- 1/10 oz Gold Eagle: 2 dwt
- 1/4 oz Gold Eagle: 5 dwt
- 1/2 oz Gold Eagle: 10 dwt
Counterfeit detection: Knowing the correct pennyweight of historic coins helps detect counterfeits: "This coin claims to be an 1893 Morgan silver dollar but weighs only 14.2 dwt instead of the correct 16.716 dwt—likely counterfeit."
5. Dental Alloys and Dentistry
Dental laboratories use pennyweights for precious metal dental alloys:
Gold crowns and bridges: Dental gold alloys (typically gold-palladium-silver combinations) are purchased and tracked in pennyweights: "Order 50 dwt of type III gold casting alloy for crown fabrication."
Scrap recovery: Dental offices collect scrap gold from old crowns, bridges, and orthodontic appliances, selling it by pennyweight to refiners: "Monthly dental scrap recovery: 18.5 dwt mixed gold alloys."
Material costs: Dental labs calculate restoration costs based on pennyweight requirements: "Three-unit bridge requires approximately 8 pennyweights of high-noble alloy, current cost $95/dwt = $760 materials."
6. Watchmaking and Repair
Watch repairmen and manufacturers use pennyweights for precious metal watch cases and components:
Gold watch cases: "18kt gold pocket watch case: 42 dwt" Solid gold bracelet links: "Replacement gold bracelet links: 1.2 dwt each" Vintage watch restoration: "Restore gold crown and stem: requires 0.8 dwt 14kt gold stock"
7. Hallmarking and Legal Compliance
Official assay offices and hallmarking authorities use pennyweights in legal documentation:
Fineness certification: British Hallmarking Act requires items over certain pennyweight thresholds be hallmarked:
- Gold: items over 0.5 dwt must be hallmarked
- Silver: items over 5 dwt must be hallmarked
- Platinum: items over 0.33 dwt must be hallmarked
Export documentation: Precious metals crossing international borders require customs declarations listing pennyweight and fineness: "Shipment: 1,450 dwt of 999 fine gold bullion."
Consumer protection: Trading standards enforce accurate weight declarations, with penalties for misrepresenting pennyweight on jewelry labels.
Additional Unit Information
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."
About Pennyweight (dwt)
How many pennyweights are in a troy ounce?
Answer: Exactly 20 pennyweights = 1 troy ounce
This is the fundamental relationship in the troy weight system. Since 1 troy ounce = 31.1035 grams and 1 pennyweight = 1.55517384 grams:
31.1035 g ÷ 1.55517384 g = 20 dwt
This makes price calculations straightforward: if gold is $2,000/troy ounce, it's exactly $100/pennyweight ($2,000 ÷ 20 = $100).
How many grains are in a pennyweight?
Answer: Exactly 24 grains = 1 pennyweight
The grain is the smallest troy weight unit, and the pennyweight was historically defined as 24 grains. This relationship has remained constant since medieval standardization:
1 dwt = 24 gr = 1.55517384 g
Since 1 grain = 64.79891 mg: 24 grains × 64.79891 mg = 1,555.17384 mg = 1.55517384 g
How many grams are in a pennyweight?
Answer: Exactly 1.55517384 grams = 1 pennyweight
This exact definition comes from the 1959 international yard and pound agreement, which defined the grain as exactly 64.79891 milligrams. Since 1 pennyweight = 24 grains:
1 dwt = 24 × 64.79891 mg = 1,555.17384 mg = 1.55517384 g (exact)
For practical purposes, you can approximate 1 dwt ≈ 1.56 g, but official transactions use the exact value.
Why is it called a "pennyweight"?
Answer: It originally represented the weight of one silver penny in medieval England
During the Anglo-Saxon period and continuing through the Norman conquest, English silver pennies were standardized to weigh exactly one pennyweight each. This created an elegant system where:
- 1 penny (coin) = 1 pennyweight (weight) of silver
- 240 pennies = 1 pound sterling = 1 troy pound of silver
This direct correspondence between monetary value and precious metal weight lasted for centuries and gave the unit its name. The abbreviation "dwt" comes from "denarius weight" (denarius being the Latin word for penny).
Is the pennyweight still used today?
Answer: Yes, the pennyweight remains the standard working unit for jewelers, goldsmiths, and precious metals dealers worldwide
Despite metrication in many countries, the pennyweight persists because:
- International trade: Precious metals are traded globally in troy ounces/pennyweights
- Industry infrastructure: Scales, pricing systems, and reference materials use troy units
- Practical size: Pennyweights provide appropriate precision for jewelry (more precise than ounces, less unwieldy than grains)
- Legal requirements: Many jurisdictions mandate troy weights for bullion and hallmarking
The London Bullion Market Association (LBMA), which sets global precious metals standards, continues to use troy ounces and pennyweights, ensuring the unit's ongoing relevance.
What's the difference between pennyweight and carat?
Answer: Pennyweight measures the weight of precious METALS, while carat measures the weight of GEMSTONES (and separately, the purity of gold)
This is a common source of confusion because "carat" has two different meanings:
1. Metric carat (ct) - Gemstone weight:
- 1 carat = 200 milligrams = 0.2 grams
- Used exclusively for gemstones (diamonds, rubies, sapphires, etc.)
- 1 pennyweight = 7.776 carats (though you wouldn't measure metal in carats)
2. Karat (kt or K) - Gold purity:
- Measures gold purity out of 24 parts
- 24kt = pure gold (99.9%)
- 18kt = 18/24 = 75% gold
- 14kt = 14/24 = 58.3% gold
- NOT a weight unit at all
Pennyweight (dwt) - Metal weight:
- 1 dwt = 1.555 grams
- Used for precious metals (gold, silver, platinum)
- A completely separate measurement from both carat meanings
Example: An "18kt gold ring weighing 5 pennyweights with a 1-carat diamond" means:
- Ring metal: 18-karat purity (75% pure gold)
- Ring weight: 5 dwt (7.78 g)
- Diamond weight: 1 carat (0.2 g)
How do I convert pennyweights to grams?
Answer: Multiply pennyweights by 1.55517384 (exact) or 1.556 (approximate)
Exact formula: grams = pennyweights × 1.55517384
Examples:
- 5 dwt = 5 × 1.55517384 = 7.7759 g
- 10 dwt = 10 × 1.55517384 = 15.5517 g
- 20 dwt = 20 × 1.55517384 = 31.1035 g (1 troy ounce)
Quick approximation: For mental math, use 1.56:
- 5 dwt ≈ 5 × 1.56 = 7.8 g (close enough for estimates)
Reverse conversion (grams to pennyweights): Divide grams by 1.55517384, or multiply by 0.643:
- 10 g ÷ 1.55517384 = 6.43 dwt
Can I use a regular scale to measure pennyweights?
Answer: No, you need a scale that displays troy units or precise gram measurements that you can convert
Most household scales show avoirdupois ounces/pounds or grams, not troy pennyweights. For accurate precious metals measurement:
Option 1: Troy weight scale
- Purchase a jeweler's scale that displays troy ounces subdivided into pennyweights
- Professional models show "oz dwt" format (e.g., "1 oz 15 dwt")
- Precision typically 0.01 dwt (0.0155 g)
Option 2: Gram scale with conversion
- Use a precise gram scale (0.01 g accuracy minimum)
- Measure in grams and divide by 1.555 to get pennyweights
- Example: 7.78 g ÷ 1.555 = 5.00 dwt
Not recommended: Regular kitchen scales or bathroom scales lack sufficient precision for pennyweight accuracy.
Professional standards: Jewelers and precious metals dealers use scales certified for troy weight accuracy, often calibrated annually to ensure compliance with trading standards regulations.
How much is a pennyweight of gold worth?
Answer: Divide the current gold price per troy ounce by 20
Gold prices are quoted in dollars per troy ounce. Since 1 troy ounce = 20 pennyweights:
Price per dwt = Price per oz t ÷ 20
Examples (using approximate gold prices):
- Gold at $2,000/oz → $100/dwt ($2,000 ÷ 20)
- Gold at $1,800/oz → $90/dwt ($1,800 ÷ 20)
- Gold at $2,200/oz → $110/dwt ($2,200 ÷ 20)
IMPORTANT: This is for pure gold (24kt). Most jewelry is alloyed:
14kt gold (58.3% pure):
- If pure gold = $100/dwt
- 14kt gold = $100 × 0.583 = $58.30/dwt
18kt gold (75% pure):
- If pure gold = $100/dwt
- 18kt gold = $100 × 0.75 = $75/dwt
Current prices: Check live gold prices at kitco.com, bullionvault.com, or your local precious metals dealer, then divide by 20 for per-pennyweight pricing.
What items typically weigh one pennyweight?
Answer: Small gold earrings, simple pendants, or single ring settings
Examples of ~1 dwt items:
- Simple gold stud earrings (pair): 0.8-1.5 dwt
- Small gold charm: 0.5-1.2 dwt
- Thin gold chain link: 0.3-0.8 dwt per link
- Single prong setting for gemstone: 0.6-1.0 dwt
- Gold nose ring/stud: 0.2-0.5 dwt
For reference:
- Medieval silver penny: exactly 1 dwt (by definition)
- Modern nickel (5¢ coin): ~32 dwt (5 g) - but not silver
- Paperclip: ~5-6 dwt (0.8 g)
Heavier items for comparison:
- Wedding ring: 3-6 dwt
- Gold chain necklace: 5-15 dwt
- Class ring: 12-20 dwt
- 1 troy ounce gold coin: 20 dwt
Why use pennyweights instead of grams for jewelry?
Answer: Industry tradition, international trade standards, and practical calculation convenience
Historical continuity: The precious metals industry has used troy weights for over 700 years. Switching to metric would require:
- Replacing millions of troy scales
- Retraining entire industry workforce
- Revising international trade agreements
- Updating hallmarking regulations in dozens of countries
International standardization: The London Bullion Market Association (LBMA) sets global precious metals trading standards in troy ounces. Since jewelry trades internationally, using consistent units (pennyweights/troy ounces) simplifies transactions.
Practical precision: Pennyweights provide appropriate precision:
- Too precise: grains (24 grains = 1 dwt means many small fractions)
- Too coarse: troy ounces (typical ring is 0.15-0.30 oz = awkward decimals)
- Just right: pennyweights (typical ring is 3-6 dwt = clean numbers)
Mental math ease: The 20:1 ratio (20 dwt = 1 oz t) makes price calculations simple:
- Gold at $2,000/oz = $100/dwt (divide by 20)
- A 5 dwt item = $500 worth of gold (multiply by 100)
Legal requirements: Many jurisdictions legally mandate troy weights for precious metals hallmarking and trading, making pennyweights the regulatory standard.
Are pennyweights used outside of precious metals?
Answer: No, pennyweights are exclusively used for precious metals, gemstone settings, and related industries
Where pennyweights ARE used:
- Gold, silver, platinum jewelry manufacturing
- Precious metals trading and refining
- Coin collecting (numismatics)
- Dental gold alloys
- Watchmaking (gold/platinum cases)
- Bullion buying and selling
- Hallmarking and assay offices
Where pennyweights are NOT used:
- General commerce (uses avoirdupois ounces/pounds or grams/kilograms)
- Food and cooking (ounces, pounds, grams)
- Body weight (pounds or kilograms)
- Gemstones themselves (use metric carats: 1 ct = 0.2 g)
- Pharmaceuticals (uses grains, grams, milligrams, but not pennyweights)
- Scientific measurements (uses metric system exclusively)
The exception: Grains (the smallest troy unit) ARE used in both troy weight (precious metals) and pharmaceutical/bullet weight measurements, but pennyweights appear only in troy contexts.
Conversion Table: Slug to Pennyweight
| Slug (sl) | Pennyweight (dwt) |
|---|---|
| 0.5 | 4,692.048 |
| 1 | 9,384.096 |
| 1.5 | 14,076.143 |
| 2 | 18,768.191 |
| 5 | 46,920.478 |
| 10 | 93,840.956 |
| 25 | 234,602.39 |
| 50 | 469,204.78 |
| 100 | 938,409.561 |
| 250 | 2,346,023.902 |
| 500 | 4,692,047.804 |
| 1,000 | 9,384,095.607 |
People Also Ask
How do I convert Slug to Pennyweight?
To convert Slug to Pennyweight, enter the value in Slug 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 Slug to Pennyweight?
The conversion factor depends on the specific relationship between Slug and Pennyweight. 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 Pennyweight back to Slug?
Yes! You can easily convert Pennyweight back to Slug by using the swap button (⇌) in the calculator above, or by visiting our Pennyweight to Slug converter page. You can also explore other weight conversions on our category page.
Learn more →What are common uses for Slug and Pennyweight?
Slug and Pennyweight 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.
Helpful Conversion Guides
Learn more about unit conversion with our comprehensive guides:
📚 How to Convert Units
Step-by-step guide to unit conversion with practical examples.
🔢 Conversion Formulas
Essential formulas for weight and other conversions.
⚖️ Metric vs Imperial
Understand the differences between measurement systems.
⚠️ Common Mistakes
Learn about frequent errors and how to avoid them.
All Weight Conversions
Other Weight Units and Conversions
Explore other weight units and their conversion options:
- Kilogram (kg) • Slug to Kilogram
- Gram (g) • Slug to Gram
- Milligram (mg) • Slug to Milligram
- Pound (lb) • Slug to Pound
- Ounce (oz) • Slug to Ounce
- Stone (st) • Slug to Stone
- Ton (metric) (t) • Slug to Ton (metric)
- Ton (US) (ton) • Slug to Ton (US)
- Ton (UK) (long ton) • Slug to Ton (UK)
- Microgram (µg) • Slug to Microgram
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 — US standards for weight and mass measurements
International Organization for Standardization — International standard for mechanics quantities
Last verified: February 19, 2026