Pound (lb) - Unit Information & Conversion

Quick Answer

What is a pound? A pound (lb) is a unit of mass equal to exactly 16 ounces or 0.45359237 kilograms. It's the fundamental weight measurement Americans use daily—from stepping on bathroom scales (150 lbs) and buying groceries ($3.99/lb) to shipping packages and describing newborn babies (7 lbs, 6 oz). While most of the world uses kilograms, the pound remains deeply embedded in American commerce, health, and everyday life.

Quick Comparison Table

Pounds	Kilograms	Ounces	Grams	Common Example	Convert Now
1 lb	0.454 kg	16 oz	454 g	Loaf of bread	Convert pounds to kg
5 lbs	2.268 kg	80 oz	2,268 g	Bag of flour or sugar	Convert pounds to oz
10 lbs	4.536 kg	160 oz	4,536 g	Bowling ball	Convert kg to pounds
50 lbs	22.68 kg	800 oz	22,680 g	Large bag of dog food	Convert pounds to grams
150 lbs	68.04 kg	2,400 oz	68,040 g	Average adult person	Convert oz to pounds
2,000 lbs	907.2 kg	32,000 oz	907,185 g	One ton (US short ton)	Convert grams to pounds

Definition

The pound is a unit of mass in the British imperial and United States customary systems of measurement. Since the international yard and pound agreement of 1959, one pound has been defined as exactly 0.45359237 kilograms. This makes the pound equal to precisely 16 ounces, 7,000 grains, or 453.59237 grams.

The pound is denoted by the symbol lb (from the Latin libra, meaning balance or scales) or sometimes lbs for plural, though technically "lb" serves both singular and plural. In commercial contexts, you'll see prices as "$/lb" (dollars per pound) or weights as "5 lb bag."

Unlike the metric system where weight relationships are decimal (1,000 grams = 1 kilogram), the pound uses the relationship of 16 ounces to 1 pound. This fractional system reflects historical divisions: 1 pound = 16 ounces = 256 drams = 7,000 grains, with each division serving practical purposes in trade and measurement.

History

The pound represents one of the oldest weight measurements in continuous use, with lineage tracing back over two millennia.

Roman Origins: The word "pound" derives from the Latin pondus (weight), while the symbol "lb" comes from libra, the Roman unit of weight equal to approximately 329 grams. The Romans used a libra divided into 12 unciae (ounces), though this differs from the modern 16-ounce pound.

Medieval Development: Multiple "pounds" existed simultaneously in medieval Europe—the tower pound (5,400 grains), merchant's pound (6,750 grains), and troy pound (5,760 grains) for precious metals. This created confusion in commerce and necessitated standardization.

Avoirdupois System: In 13th-century England, the avoirdupois system (from Old French aver de peis, "goods of weight") emerged for general commerce. The avoirdupois pound standardized at 16 ounces, each containing 437.5 grains, totaling 7,000 grains per pound. This system proved so practical for trade that it displaced most other pound definitions.

British Standardization: The Weights and Measures Act of 1824 established the imperial pound throughout the British Empire, legally defining it through physical standards. The Imperial Standard Pound, a platinum cylinder, was kept at the Houses of Parliament as the official definition.

US Independence: After the American Revolution, the United States maintained the British pound definition from colonial times. The Mendenhall Order of 1893 tied US weights to metric standards: 1 pound = 0.4535924277 kilograms (based on 1 meter = 39.37 inches).

1959 International Agreement: The international yard and pound agreement unified English-speaking nations. The United States, United Kingdom, Canada, Australia, New Zealand, and South Africa agreed that 1 pound equals exactly 0.45359237 kilograms. This created perfect mathematical alignment between imperial and metric systems.

Troy vs. Avoirdupois: Two pound systems coexist today. The avoirdupois pound (16 oz, 453.6 g) is used for general commerce and everyday measurements. The troy pound (12 troy oz, 373.2 g) survives only for precious metals—gold, silver, platinum. When someone says "pound" without qualifier, they always mean avoirdupois pound.

Cultural Persistence: Despite metric conversion efforts worldwide, the pound persists in American daily life. The 1975 Metric Conversion Act made metric "preferred" but voluntary, allowing continued pound usage. Today, Americans buy meat in pounds, weigh themselves in pounds, and ship packages in pounds, maintaining a measurement tradition spanning centuries.

Real-World Examples

Human Body Weight

The pound is the universal body weight measurement in the United States:

• Newborn baby: 6-9 lbs (average 7 lbs, 8 oz)
• 1-year-old child: 20-22 lbs
• 5-year-old child: 40-50 lbs
• 10-year-old child: 70-90 lbs
• Average adult woman (US): 170 lbs
• Average adult man (US): 200 lbs
• Healthy BMI range (5'9" person): 125-169 lbs
• Heavyweight boxer limit: 200+ lbs
• NFL lineman: 300-350 lbs (common)
• World's strongest man competitors: 350-450 lbs

Americans describe body weight exclusively in pounds, often shortened conversationally: "I weigh one-fifty" (150 lbs) or "He's over two hundred" (200+ lbs). Medical professionals in the US record weight in pounds, though hospital systems increasingly capture kilograms as well for medication dosing.

Grocery Store Produce and Meat

Supermarkets in the US price and sell food by the pound:

Produce:

• Apples: $1.99-2.99/lb (about 3 medium apples per pound)
• Bananas: $0.59-0.89/lb (about 3-4 bananas per pound)
• Tomatoes: $2.49-3.99/lb
• Potatoes: $0.99-1.99/lb (russet potatoes, 5-lb bags common)
• Grapes: $2.99-4.99/lb
• Strawberries: Often sold in 1-lb containers

Meat Counter:

• Ground beef: $4.99-7.99/lb depending on fat percentage
• Chicken breast: $3.99-6.99/lb boneless/skinless
• Pork chops: $3.49-5.99/lb
• Ribeye steak: $12.99-19.99/lb
• Salmon fillet: $9.99-14.99/lb
• Deli turkey: $7.99-12.99/lb sliced

Bulk Items:

• Flour: 5-lb bag (most common), 10-lb, 25-lb, 50-lb bags
• Sugar: 4-lb bag, 5-lb, 10-lb bags
• Rice: 5-lb, 10-lb, 20-lb bags
• Dog food: 15-lb, 30-lb, 40-lb bags

Grocery scales display weight in pounds and ounces (5 lbs, 3 oz), and customers intuitively understand "about a half-pound" or "just over two pounds" for produce selection.

Infant and Newborn Weights

Newborn babies are always described in pounds and ounces in the US:

• Average birth weight: 7 lbs, 6 oz (7.375 lbs)
• Low birth weight: Under 5 lbs, 8 oz
• Very low birth weight: Under 3 lbs, 5 oz
• Premature twins: Often 4-5 lbs each at birth
• Large newborn: 9-10+ lbs

Parents track infant weight gain in ounces during the first months, then pounds as the child grows. Pediatric growth charts in the US show both pounds and kilograms, but doctors and parents discuss weight in pounds: "She's up to 15 pounds" or "He gained half a pound this week."

Package and Luggage Weight

Shipping and travel use pounds for weight limits:

Postal Service (USPS):

• First-Class Mail: Up to 13 oz (then switches to Priority)
• Priority Mail: Up to 70 lbs
• Media Mail: Up to 70 lbs
• Parcel Select: Up to 70 lbs

Airline Baggage:

• Carry-on weight: Typically no limit (US domestic), 15-22 lbs (international)
• Checked bag standard: 50 lbs (most US airlines)
• Overweight fee threshold: 51-70 lbs (additional $50-100 fee)
• Heavy bag limit: 100 lbs maximum (some airlines refuse heavier)

Shipping Carriers:

• UPS/FedEx Ground: Up to 150 lbs per package
• UPS/FedEx freight: Over 150 lbs (requires special handling)

Travelers weigh luggage before airport trips, aiming to stay under 50 lbs to avoid overweight fees. A bathroom scale showing "48 lbs" means safe to check; "52 lbs" means remove items or pay fees.

Pets and Animals

Veterinary care and pet descriptions use pounds:

Dogs:

• Chihuahua: 3-6 lbs
• Dachshund: 16-32 lbs
• Beagle: 20-30 lbs
• Border Collie: 30-55 lbs
• Labrador Retriever: 55-80 lbs
• Golden Retriever: 55-75 lbs
• German Shepherd: 50-90 lbs
• Great Dane: 110-175 lbs
• English Mastiff: 150-230 lbs

Cats:

• Siamese: 8-12 lbs
• Domestic shorthair: 10-15 lbs
• Maine Coon: 12-25 lbs (largest domestic cat breed)

Livestock:

• Market hog: 250-280 lbs (typical slaughter weight)
• Feeder calf: 500-800 lbs
• Market steer: 1,200-1,400 lbs
• Dairy cow: 1,000-1,500 lbs
• Quarter horse: 1,000-1,200 lbs

Pet owners monitor animal weight for health: "The vet said she needs to lose 3 pounds" or "He's finally up to 8 pounds after being sick."

Fitness and Exercise Equipment

Gym equipment uses pounds for resistance:

Free Weights:

• Dumbbells: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100+ lbs
• Barbell (standard): 45 lbs (Olympic bar)
• Weight plates: 2.5, 5, 10, 25, 35, 45 lbs

Exercise Milestones:

• Beginner bench press: 95 lbs (45-lb bar + two 25-lb plates)
• Intermediate bench press: 185 lbs (45-lb bar + two 45-lb plates + two 25-lb plates)
• Advanced bench press: 225+ lbs (45-lb bar + four 45-lb plates)
• Squat/deadlift targets often 50-100 lbs higher than bench press

Resistance Machines:

• Weight stacks in 10-lb or 15-lb increments
• Cable machines calibrated in pounds
• Leg press can load 500-1,000+ lbs

Fitness enthusiasts track "personal records" (PRs) in pounds: "Hit a new PR on deadlifts—405 pounds!" Weight progression follows predictable increments: add 5 lbs upper body, 10 lbs lower body each session.

Fishing and Hunting

Outdoor sports describe catches and game in pounds:

Fishing:

• Panfish (bluegill, crappie): 0.25-0.5 lbs
• Bass (largemouth): 1-5 lbs (trophy: 8+ lbs)
• Trout: 0.5-3 lbs typical
• Catfish: 5-50 lbs (blue catfish can exceed 100 lbs)
• Salmon: 8-30 lbs depending on species
• Marlin: 200-1,000+ lbs
• Tuna (bluefin): 200-1,500 lbs

Fishing line strength rates in "pound-test": 6-lb test for panfish, 15-20 lb test for bass, 50-100+ lb test for big game saltwater fishing. "Pound-test" indicates the breaking strength in pounds of force.

Hunting:

• Wild turkey: 15-25 lbs
• White-tailed deer: 100-300 lbs (bucks typically heavier)
• Wild boar: 150-400 lbs
• Elk: 500-1,000 lbs (bulls)
• Moose: 800-1,500 lbs (bulls)

Hunters describe harvests by weight: "Got a 180-pound buck this season" or field-dressed weight (after removing organs): "Field-dressed at 140 pounds."

Building Materials and Hardware

Construction materials specify weight in pounds:

Bags of Materials:

• Portland cement: 94-lb bag (standard)
• Concrete mix: 40-lb, 60-lb, 80-lb bags
• Mortar mix: 60-lb, 80-lb bags
• Tile grout: 25-lb bag
• Tile thinset: 50-lb bag
• Stucco: 80-lb bag

Sheet Materials:

• Drywall (1/2"): 2 lbs per square foot (4×8 sheet = 64 lbs)
• Plywood (3/4"): 2.3 lbs per square foot (4×8 sheet = 74 lbs)
• Oriented strand board (OSB): Similar to plywood

Roofing:

• Asphalt shingles: 50-lb bundles (covers ~33 sq ft)
• Roofing felt: 15-lb or 30-lb felt (per 100 sq ft coverage)

Contractors calculate material handling needs based on weight: two workers to carry a sheet of 3/4" plywood (74 lbs), solo carry for drywall sheets (manageable at 50-60 lbs depending on thickness).

Sports Equipment

Athletic equipment weights are standardized in pounds:

Balls:

• Baseball: 5-5.25 oz (about 0.32 lbs)
• Softball: 6.25-7 oz (about 0.44 lbs)
• Basketball: 20-22 oz (about 1.38 lbs)
• Football: 14-15 oz (about 0.94 lbs)
• Bowling ball: 6-16 lbs (regulation range, most adults use 12-15 lbs)
• Shot put (high school boys): 12 lbs
• Shot put (men): 16 lbs

Protective Gear:

• Hockey goalie pads: 25-35 lbs complete set
• Football shoulder pads: 3-6 lbs
• Catcher's gear (baseball): 15-20 lbs complete
• Boxing gloves: 8 oz, 10 oz, 12 oz, 14 oz, 16 oz (competition vs. training)

Exercise Equipment:

• Kettlebells: 10, 15, 20, 25, 35, 45, 55, 70 lbs
• Medicine balls: 2, 4, 6, 8, 10, 12, 15, 20 lbs
• Weight vest: 10-50 lbs (adjustable)

Athletes select equipment based on strength and skill level: beginners use 12-lb bowling balls, experienced bowlers use 14-16 lbs for better pin action.

Common Uses

Medical and Healthcare Settings

Healthcare in the US primarily operates in pounds for patient weight, though hospitals increasingly record kilograms for medication dosing calculations. Patient charts typically show both: "185 lbs (84 kg)." However, all patient communication uses pounds—doctors say "You've gained 5 pounds" or "Try to lose 10-15 pounds," never kilograms.

Weight-based medication dosing creates complexity: drugs dose in mg/kg, requiring conversion. A 160-lb patient equals 72.6 kg, so a drug dosed at 5 mg/kg requires 363 mg. Medical staff use conversion charts or electronic calculators to prevent errors.

Anesthesiology requires precise weight for medication dosing. Operating room scales display both pounds and kilograms, with staff typically asking patients "What's your weight in pounds?" for verification against chart data.

Public health BMI calculations use pounds and inches in the US: BMI = (weight in pounds × 703) ÷ (height in inches)². A person 5'9" (69") weighing 170 lbs has BMI = (170 × 703) ÷ (69 × 69) = 25.1, just into the "overweight" category (BMI 25-29.9).

Weight Loss and Fitness Industry

Diet programs, weight loss apps, and fitness tracking exclusively use pounds in the US market. Weight Watchers, MyFitnessPal, Lose It!, and similar apps default to pounds, though users can switch to kilograms.

Fitness goals frame in pounds: "Lose 20 pounds by summer," "Gain 10 pounds of muscle," "Drop 5 pounds this month." Personal trainers track client progress in pounds, celebrating milestone losses: "You've lost 25 pounds—that's like losing two bowling balls!"

Scale psychology creates significance for specific numbers. Dropping below 200 lbs (reaching "onederland") represents a major milestone for many dieters. Breaking into the 100s (199 lbs) feels dramatically different from 200 lbs despite being only 1 pound difference.

Bodybuilding competitions divide by weight classes in pounds: lightweight (<154 lbs), middleweight (154-176 lbs), light-heavyweight (176-198 lbs), heavyweight (198-242 lbs), super-heavyweight (>242 lbs). Competitors cut weight aggressively, sometimes losing 10-20 lbs of water weight in final days before weigh-in.

Commercial Food Service and Restaurants

Restaurant kitchens order ingredients in pounds and bulk quantities:

• 50-lb bags of onions
• 40-lb cases of chicken breast
• 25-lb blocks of cheese
• 5-lb containers of mayonnaise
• 10-lb boxes of bacon

Recipe scaling in commercial kitchens calculates in pounds: a recipe serving 20 using 2 lbs ground beef scales to serve 100 by using 10 lbs. Kitchen scales measure in pounds and ounces, with precision to 0.1 oz for small quantities.

Food costs calculate per pound: if chicken costs $2.50/lb and a dish uses 6 oz (0.375 lbs), the protein cost is $0.94 per serving. Restaurant profitability depends on accurate food costing, requiring staff to think fluently in pounds and ounces.

Portion control uses ounces: 8-oz steak, 6-oz salmon fillet, 4-oz burger patty (quarter-pounder). Pre-portioned proteins simplify cooking and ensure consistency. A case of forty 4-oz burger patties weighs 10 lbs total.

Postal and Freight Shipping

The entire US shipping industry operates in pounds. Postage rates tier by weight:

USPS First-Class Mail:

• Up to 3 oz: $0.63 (letter)
• Up to 13 oz: Incrementally increases
• Over 13 oz: Requires Priority Mail

Priority Mail tiers:

• Up to 1 lb: $8.50 flat rate (approximate regional)
• 1-2 lbs: $9.50
• 2-3 lbs: $11.00
• Continues in 1-lb increments to 70 lbs

Shipping costs increase dramatically with weight. A 15.5-lb package costs significantly more than a 15-lb package if it crosses a tier boundary. Online sellers optimize packaging to stay within weight tiers: use lighter boxes, remove unnecessary materials, choose compact packaging.

Freight shipping (over 150 lbs) charges by "hundredweight" (CWT): cost per 100 lbs. A 750-lb shipment traveling 500 miles at $45/CWT costs $337.50 (7.5 × $45).

Farming and Agriculture

Agricultural commerce operates entirely in pounds:

Crop yields per acre:

• Corn: 170-200 bushels/acre (56 lbs per bushel = 9,520-11,200 lbs/acre)
• Soybeans: 50-60 bushels/acre (60 lbs per bushel = 3,000-3,600 lbs/acre)
• Wheat: 50-70 bushels/acre (60 lbs per bushel = 3,000-4,200 lbs/acre)

Livestock weights:

• Market hogs: Sold at 250-280 lbs live weight
• Feeder cattle: Sold at 600-800 lbs, finished at 1,200-1,400 lbs
• Broiler chickens: Processed at 5-6 lbs
• Turkeys: Processed at 25-30 lbs

Feed calculations:

• Dairy cow eats 50-60 lbs of feed daily
• Beef cattle eat 25-30 lbs of feed daily during finishing
• Horse eats 15-25 lbs of hay daily
• Bag of horse feed: 50 lbs (common size)

Farmers sell crops and livestock by the pound or hundredweight (100 lbs). Commodity prices quote in cents per pound: corn at $0.055/lb, soybeans at $0.15/lb (converted from bushel prices).

Manufacturing and Industrial Production

Manufacturing specs, especially for non-precision work, use pounds:

Sheet metal weight:

• Steel sheet weight: pounds per square foot for given thickness
• Aluminum sheet: Lighter than steel at same thickness
• Copper sheet: Heavier than steel

Material handling:

• Pallet weight limits: 2,500 lbs typical
• Forklift capacity: 3,000-5,000 lbs common
• Hand truck/dolly: 500-800 lbs capacity

Product specifications:

• Appliances: Refrigerator 200-300 lbs, washing machine 150-200 lbs
• Furniture: Dining table 50-150 lbs, dresser 100-200 lbs
• Machinery: Small lathe 500-1,500 lbs, mill 2,000-5,000 lbs

Shipping and logistics calculate by weight and dimensions. Freight classifications assign classes based on weight density (pounds per cubic foot): class 50 (50+ lbs/cu ft, densest), class 500 (1 lb/cu ft, lightest).

Waste Management and Recycling

Waste services charge based on weight:

Dumpster weight limits:

• 10-yard dumpster: 2-3 tons (4,000-6,000 lbs) weight limit
• 20-yard dumpster: 3-4 tons (6,000-8,000 lbs)
• 40-yard dumpster: 5-6 tons (10,000-12,000 lbs)

Exceeding weight limits incurs fees: $50-100 per ton over limit. Construction debris (concrete, brick, dirt) quickly exceeds weight limits despite not filling volume.

Recycling programs:

• Aluminum cans: ~30 cans per pound, recyclers pay $0.30-0.50/lb
• Scrap steel: $0.05-0.15/lb
• Copper: $2-4/lb (valuable, often stolen)
• Cardboard: $0.02-0.10/lb
• Paper: $0.01-0.05/lb

Individuals recycling metals weigh loads at scrap yards on drive-over scales, receiving payment based on total pounds by category.

Pet Care and Veterinary Medicine

Pet food portion recommendations use pounds:

• Small dogs (<20 lbs): 1/2 to 1 cup food daily
• Medium dogs (20-50 lbs): 1 to 2 cups daily
• Large dogs (50-90 lbs): 2 to 3.5 cups daily
• Giant dogs (>90 lbs): 3.5 to 5+ cups daily

Medication dosing requires accurate pet weight. A 40-lb dog receiving medication at 1 mg/lb needs a 40 mg dose. Underdosing proves ineffective; overdosing risks toxicity.

Veterinarians track pet weight over time, flagging unhealthy gains or losses. "Fluffy has gained 3 pounds since last year—we need to reduce portions" or "Max has lost 5 pounds unexpectedly—let's run some tests."

Common Conversion Mistakes to Avoid

Mistake 1: Confusing Pounds with Kilograms in Medical Contexts

The Error: A patient weighing 75 kilograms self-reports as "75 pounds" on medical forms, or staff mistakenly enter "75 lbs" instead of "75 kg" in computer systems.

Why It Happens: International patients or immigrants from metric countries think in kilograms but see forms requesting pounds, creating confusion. Electronic medical records sometimes default to pounds but accept numerical input without unit verification.

The Reality: 75 kg = 165 lbs (not 75 lbs). This error creates dramatic medication dosing mistakes. A patient actually weighing 165 lbs given medication dosed for 75 lbs receives less than half the required dose. Conversely, a 75-lb child mistakenly recorded as 75 kg (165 lbs) could receive double the safe dose—potentially fatal.

How to Avoid: Medical facilities implement double-checks: ask patients their weight and verify "Is that in pounds or kilograms?" Electronic systems should force unit selection rather than assuming. Staff should question implausible values: an adult "75 lbs" or child "150 lbs" warrant verification. Always convert and display both units: "165 lbs (75 kg)" prevents confusion.

Mistake 2: Rounding Kilogram Conversions Too Aggressively

The Error: Converting weight using "2 pounds per kilogram" or "divide by 2 to get kilograms," introducing 10%+ errors.

Why It Happens: People learn rough conversions like "a kilogram is about 2 pounds" for quick mental math, but apply these approximations where precision matters.

The Reality: One pound equals exactly 0.45359237 kilograms (not 0.5):

• 100 lbs = 45.36 kg (not 50 kg)
• 200 lbs = 90.72 kg (not 100 kg)
• 150 lbs = 68.04 kg (not 75 kg)

For reverse conversion, multiply kilograms by 2.20462 (not 2):

• 100 kg = 220.46 lbs (not 200 lbs)
• 75 kg = 165.35 lbs (not 150 lbs)

How to Avoid: Use exact conversion factors (0.45359237 or 2.20462) when precision matters: medication dosing, aircraft weight and balance, engineering specifications, commercial trade. For rough estimates, remember 1 kg ≈ 2.2 lbs (slightly more than 2), or 10 lbs ≈ 4.5 kg. Never use rough approximations in medical, aviation, or legal contexts.

Mistake 3: Adding Pounds and Ounces Without Proper Conversion

The Error: Adding 5 lbs 10 oz + 3 lbs 8 oz = 8 lbs 18 oz instead of converting excess ounces to pounds.

Why It Happens: People treat pounds and ounces as separate numbers and add them independently, forgetting that 16 ounces equals 1 pound. The notation "8 lbs 18 oz" appears mathematically correct but isn't standard because 18 exceeds 16 ounces.

The Reality: You must convert excess ounces to pounds:

• 5 lbs 10 oz + 3 lbs 8 oz = 8 lbs + 18 oz
• 18 oz = 16 oz + 2 oz = 1 lb + 2 oz
• Final answer: 9 lbs 2 oz

Alternatively, convert entirely to ounces: 5 lbs 10 oz = 90 oz, 3 lbs 8 oz = 56 oz, total = 146 oz = 9 lbs 2 oz.

How to Avoid: Always convert ounces to pounds when ounces exceed 16. Use a kitchen scale displaying decimal pounds (9.125 lbs = 9 lbs 2 oz) to avoid fraction math, or convert all weights to ounces, calculate, then convert back.

Mistake 4: Misunderstanding Stone Measurements from UK

The Error: Hearing someone from the UK say "I weigh 12 stone" and thinking they weigh 12 pounds.

Why It Happens: The stone is a UK weight unit unfamiliar to most Americans. People hear "stone" and don't know how to convert, sometimes guessing wildly.

The Reality: One stone = 14 pounds. A person weighing "12 stone" weighs 12 × 14 = 168 pounds. UK residents commonly express body weight in stones and pounds: "12 stone 6" means 12 stone + 6 lbs = 168 + 6 = 174 lbs total.

Common stone weights:

• 10 stone = 140 lbs
• 11 stone = 154 lbs
• 12 stone = 168 lbs
• 13 stone = 182 lbs
• 14 stone = 196 lbs
• 15 stone = 210 lbs

How to Avoid: Remember that stones are significantly heavier than pounds (14× heavier). When communicating with UK residents, ask for clarification: "Is that in stone or pounds?" Modern UK health systems increasingly use kilograms to align with international standards, reducing confusion.

Mistake 5: Confusing Troy Pounds with Avoirdupois Pounds

The Error: Assuming all pounds are equal, without realizing precious metals use a different pound definition.

Why It Happens: The word "pound" appears without qualification, and most people don't know multiple pound systems exist. Troy pounds survive exclusively for precious metals (gold, silver, platinum), while avoirdupois pounds handle everything else.

The Reality:

• Avoirdupois pound: 16 ounces = 453.592 grams (standard pound)
• Troy pound: 12 troy ounces = 373.242 grams (precious metals only)

A troy pound is about 82% of an avoirdupois pound (373g vs. 454g). Precious metals actually quote prices per troy ounce (31.1 grams), not per troy pound. Gold at $2,000/troy ounce would be $24,000/troy pound.

How to Avoid: Unless discussing precious metals, assume "pound" means avoirdupois pound (16 oz, 454g). Precious metals industry always specifies "troy ounce" or simply "ounce" (meaning troy). When purchasing gold or silver, confirm pricing per troy ounce (31.1g), not per gram or avoirdupois ounce (28.35g).

Mistake 6: Incorrect Weight-to-Volume Conversions

The Error: Assuming "a pound of water equals a pint" or "8 pounds equals a gallon" applies to all liquids and materials.

Why It Happens: The phrase "a pint's a pound the world around" teaches that a pint of water weighs approximately one pound. People overgeneralize this to all substances.

The Reality: This approximation works only for water and watery liquids near room temperature:

• 1 pint water = 1.043 lbs (close enough to 1 lb for rough estimates)
• 1 gallon water = 8.34 lbs (not exactly 8 lbs)

Other liquids differ significantly:

• 1 gallon milk = 8.6 lbs (denser than water)
• 1 gallon gasoline = 6.0-6.3 lbs (less dense than water)
• 1 gallon honey = 12 lbs (much denser)
• 1 gallon motor oil = 7.5 lbs

Solids vary dramatically:

• 1 cup flour = 4.5 oz = 0.28 lbs (not 0.5 lbs like a cup of water)
• 1 cup sugar = 7 oz = 0.44 lbs
• 1 cup butter = 8 oz = 0.5 lbs

How to Avoid: Never assume weight equals volume unless dealing specifically with water. Each material has a unique density (weight per volume). Recipes specify "1 cup flour (4.5 oz)" for precision. For liquids other than water, look up specific gravity or density for accurate conversions.