Pounds, Kilograms & More
Last reviewed: May 2026
Convert between imperial (ounces, pounds, tons) and metric (grams, kilograms, metric tons) weight units, plus specialty units like stones and troy ounces. The most common conversion — pounds to kilograms — comes up in health, shipping, cooking, and international commerce.1
| From | To | Multiply By |
|---|---|---|
| Pounds | Kilograms | 0.45359 |
| Ounces | Grams | 28.3495 |
| Stones | Pounds | 14 |
| Kilograms | Pounds | 2.20462 |
| Grams | Ounces | 0.03527 |
| Short ton | Metric ton | 0.90718 |
Weight and mass are technically different — mass is the amount of matter (constant everywhere), while weight is the force of gravity on that mass (varies by location). On Earth's surface, the distinction is academic for everyday use. The two major systems: Imperial/U.S. customary uses pounds (lbs) and ounces (oz), and Metric (SI) uses kilograms (kg) and grams (g). The fundamental conversion: 1 kg = 2.20462 lbs. The U.S. is one of three countries (with Myanmar and Liberia) that hasn't officially adopted the metric system for everyday use.
1 kilogram = 2.205 pounds = 35.274 ounces. 1 pound = 0.4536 kilograms = 453.6 grams = 16 ounces. 1 ounce = 28.35 grams. 1 stone = 14 pounds = 6.35 kg (used in the UK for body weight). 1 metric ton = 1,000 kg = 2,205 lbs. 1 U.S. ton = 2,000 lbs = 907.2 kg. Quick mental math: to convert kg to lbs, double and add 10% — 70 kg × 2 = 140, + 14 = 154 lbs (actual: 154.3).
Body weight: Medical contexts worldwide use kilograms. Drug dosing, BMI calculation, and anesthesia protocols all require kg. The UK uniquely uses stones and pounds for casual body weight ("I weigh 12 stone 4" = 172 lbs = 78 kg). Food and cooking: Metric countries weigh ingredients in grams; the U.S. uses ounces and cups. Shipping: International shipping uses kilograms; domestic U.S. carriers use pounds. Dimensional weight (package size converted to weight) may exceed actual weight for large, light packages. Precious metals: Gold and silver use troy ounces (31.1g), not avoirdupois ounces (28.35g) — a troy ounce is 10% heavier.
The metric system's strength is its decimal base: 1 kg = 1,000 g, 1 g = 1,000 mg. Moving between scales requires only shifting a decimal point. The Imperial system has no consistent relationship: 1 pound = 16 ounces, 1 ton = 2,000 pounds, 1 ounce = 16 drams. This inconsistency creates errors — the Mars Climate Orbiter was lost in 1999 because one engineering team used pounds and another used newtons, a $328 million mistake.
Daily weight fluctuates 2-6 pounds (1-3 kg) based on hydration, food volume in the digestive system, sodium intake, and hormonal cycles. A single weigh-in is meaningless — trends over 7-14 day averages reveal true changes. For weight management, weigh yourself at the same time daily (morning, after bathroom, before eating) and track the weekly moving average. A consistent 1-2 lb/week downtrend in the average indicates real fat loss; day-to-day fluctuations are noise.
The kilogram was the last SI base unit defined by a physical artifact — the International Prototype of the Kilogram (IPK), a platinum-iridium cylinder stored at the BIPM in France since 1889. In 2019, the kilogram was redefined based on the Planck constant, a fundamental property of nature. This change ensures that the kilogram never shifts — the IPK had gained approximately 50 micrograms over its lifetime from surface contamination. Consumer scales are far less precise: most kitchen scales are accurate to ±1-2 grams, bathroom scales to ±0.5-1 lb, and shipping scales to ±0.1 lb.
Carats: Used for gemstones, 1 carat = 200 milligrams = 0.007 ounces. A 1-carat diamond weighs the same as a small paperclip. Grains: Used in ammunition and pharmacy, 1 grain = 64.8 milligrams. Aspirin tablets are typically 325 mg (5 grains). Pennyweight: Used in jewelry, 1 dwt = 1.555 grams = 1/20 of a troy ounce. Long tons: UK measurement, 1 long ton = 2,240 lbs (versus 2,000 lbs for a U.S. short ton). Metric carats: Used for gold purity, but "karat" (spelled with K) refers to purity fraction (24K = pure gold), not weight.
When a scale isn't available, reference objects help estimate weight. A U.S. nickel weighs exactly 5 grams. A U.S. dollar bill weighs approximately 1 gram. A medium apple weighs roughly 200 grams (7 oz). A liter of water weighs exactly 1 kilogram (2.2 lbs). A standard brick weighs about 5 lbs (2.3 kg). These reference points help with cooking, mailing packages, and checking luggage weight before heading to the airport.
USPS, UPS, and FedEx use both actual weight and dimensional weight (DIM weight), charging whichever is greater. DIM weight = (L × W × H in inches) ÷ divisor (typically 139 for USPS/UPS domestic). A 24"×18"×12" box that weighs 5 lbs has a DIM weight of 24×18×12÷139 = 37 lbs — you'd be charged for 37 lbs, not 5. This is why packaging should be right-sized to contents. International shipping uses the metric system: USPS charges by kg; most international carriers round up to the nearest 0.5 kg. The difference between 2.1 kg and 2.5 kg can be a $5-15 cost difference for international parcels.
A common confusion: food weight includes water content, but nutritional density varies dramatically per gram. 100g of chicken breast provides ~165 calories and 31g protein. 100g of cheddar cheese provides ~403 calories and 25g protein. 100g of lettuce provides ~15 calories. When nutrition labels say "serving size: 85g," that's the raw weight — cooked meat loses 25-30% of its weight to moisture evaporation, so 85g raw becomes roughly 60-65g cooked. If you weigh portions for calorie tracking, specify whether you're weighing raw or cooked and use the corresponding nutrition data.
In everyday language, weight and mass are interchangeable — but in science, engineering, and international trade, the distinction matters. Mass measures the amount of matter in an object and doesn't change with location: a 70 kg person has 70 kg of mass on Earth, the Moon, or the International Space Station. Weight is the force gravity exerts on that mass — on the Moon (1/6 Earth gravity), the same person weighs only 11.7 kg-force. This distinction affects calibration of scales: a spring scale measures weight (force) and gives different readings at different altitudes, while a balance scale compares masses and works identically everywhere. For precision applications like pharmaceutical compounding, laboratory work, and gemstone trading, instruments must be calibrated for local gravitational acceleration, which varies from 9.764 to 9.834 m/s² across Earth's surface — enough to create measurable discrepancies on analytical balances reading to 0.001 grams.
English-speaking countries historically used three different pound systems simultaneously. The avoirdupois pound (16 ounces, 453.592 grams) is the standard for general commerce — when a recipe says "one pound of butter," this is the system. The troy pound (12 troy ounces, 373.242 grams) is used exclusively for precious metals and gemstones: a troy ounce is 31.103 grams versus 28.350 grams for a standard (avoirdupois) ounce. This means a "pound" of gold (373g) actually weighs less than a "pound" of feathers (454g), despite the famous riddle implying they're the same. The apothecary system, once used by pharmacists, measured in grains (64.799 mg), scruples (20 grains), drams (3 scruples), and ounces (8 drams). Modern pharmacy has fully converted to metric, but you may encounter grain measurements on older medication dosages — aspirin was traditionally dosed at 5 grains (325 mg).
In logistics, the billable weight of a shipment is not always its actual weight. Carriers calculate dimensional weight (also called volumetric weight) by multiplying length × width × height and dividing by a dimensional factor — typically 5,000 for metric measurements (cm/kg) or 139 for imperial (inches/lbs). The carrier charges whichever is higher: actual weight or dimensional weight. A large, lightweight package (like a box of pillows measuring 60×50×40 cm weighing 5 kg) has a dimensional weight of 24 kg — nearly five times its actual weight — and is billed accordingly. This system exists because cargo planes and trucks run out of space before they run out of weight capacity with lightweight goods. Understanding dimensional weight explains why shipping costs for bulky items seem disproportionately high and why compact packaging saves real money: reducing a box from 60×50×40 to 50×40×30 cm cuts dimensional weight from 24 kg to 12 kg, potentially halving shipping costs while the actual contents haven't changed at all.
In everyday language, weight and mass are interchangeable — but in science, engineering, and international trade, the distinction matters. Mass measures the amount of matter in an object and doesn't change with location: a 70 kg person has 70 kg of mass on Earth, the Moon, or the International Space Station. Weight is the force gravity exerts on that mass — on the Moon (1/6 Earth gravity), the same person weighs only 11.7 kg-force. This distinction affects calibration of scales: a spring scale measures weight (force) and gives different readings at different altitudes, while a balance scale compares masses and works identically everywhere. For precision applications like pharmaceutical compounding, laboratory work, and gemstone trading, instruments must be calibrated for local gravitational acceleration, which varies from 9.764 to 9.834 m/s² across Earth's surface — enough to create measurable discrepancies on analytical balances reading to 0.001 grams.
English-speaking countries historically used three different pound systems simultaneously. The avoirdupois pound (16 ounces, 453.592 grams) is the standard for general commerce — when a recipe says "one pound of butter," this is the system. The troy pound (12 troy ounces, 373.242 grams) is used exclusively for precious metals and gemstones: a troy ounce is 31.103 grams versus 28.350 grams for a standard (avoirdupois) ounce. This means a "pound" of gold (373g) actually weighs less than a "pound" of feathers (454g), despite the famous riddle implying they're the same. The apothecary system, once used by pharmacists, measured in grains (64.799 mg), scruples (20 grains), drams (3 scruples), and ounces (8 drams). Modern pharmacy has fully converted to metric, but you may encounter grain measurements on older medication dosages — aspirin was traditionally dosed at 5 grains (325 mg).
In logistics, the billable weight of a shipment is not always its actual weight. Carriers calculate dimensional weight (also called volumetric weight) by multiplying length × width × height and dividing by a dimensional factor — typically 5,000 for metric measurements (cm/kg) or 139 for imperial (inches/lbs). The carrier charges whichever is higher: actual weight or dimensional weight. A large, lightweight package (like a box of pillows measuring 60×50×40 cm weighing 5 kg) has a dimensional weight of 24 kg — nearly five times its actual weight — and is billed accordingly. This system exists because cargo planes and trucks run out of space before they run out of weight capacity with lightweight goods. Understanding dimensional weight explains why shipping costs for bulky items seem disproportionately high and why compact packaging saves real money: reducing a box from 60×50×40 to 50×40×30 cm cuts dimensional weight from 24 kg to 12 kg, potentially halving shipping costs while the actual contents haven't changed at all.
In everyday language, weight and mass are interchangeable — but in science, engineering, and international trade, the distinction matters. Mass measures the amount of matter in an object and doesn't change with location: a 70 kg person has 70 kg of mass on Earth, the Moon, or the International Space Station. Weight is the force gravity exerts on that mass — on the Moon (1/6 Earth gravity), the same person weighs only 11.7 kg-force. This distinction affects calibration of scales: a spring scale measures weight (force) and gives different readings at different altitudes, while a balance scale compares masses and works identically everywhere. For precision applications like pharmaceutical compounding, laboratory work, and gemstone trading, instruments must be calibrated for local gravitational acceleration, which varies from 9.764 to 9.834 m/s² across Earth's surface — enough to create measurable discrepancies on analytical balances reading to 0.001 grams.
English-speaking countries historically used three different pound systems simultaneously. The avoirdupois pound (16 ounces, 453.592 grams) is the standard for general commerce — when a recipe says "one pound of butter," this is the system. The troy pound (12 troy ounces, 373.242 grams) is used exclusively for precious metals and gemstones: a troy ounce is 31.103 grams versus 28.350 grams for a standard (avoirdupois) ounce. This means a "pound" of gold (373g) actually weighs less than a "pound" of feathers (454g), despite the famous riddle implying they're the same. The apothecary system, once used by pharmacists, measured in grains (64.799 mg), scruples (20 grains), drams (3 scruples), and ounces (8 drams). Modern pharmacy has fully converted to metric, but you may encounter grain measurements on older medication dosages — aspirin was traditionally dosed at 5 grains (325 mg).
In logistics, the billable weight of a shipment is not always its actual weight. Carriers calculate dimensional weight (also called volumetric weight) by multiplying length × width × height and dividing by a dimensional factor — typically 5,000 for metric measurements (cm/kg) or 139 for imperial (inches/lbs). The carrier charges whichever is higher: actual weight or dimensional weight. A large, lightweight package (like a box of pillows measuring 60×50×40 cm weighing 5 kg) has a dimensional weight of 24 kg — nearly five times its actual weight — and is billed accordingly. This system exists because cargo planes and trucks run out of space before they run out of weight capacity with lightweight goods. Understanding dimensional weight explains why shipping costs for bulky items seem disproportionately high and why compact packaging saves real money: reducing a box from 60×50×40 to 50×40×30 cm cuts dimensional weight from 24 kg to 12 kg, potentially halving shipping costs while the actual contents haven't changed at all.
In everyday language, weight and mass are interchangeable — but in science, engineering, and international trade, the distinction matters. Mass measures the amount of matter in an object and doesn't change with location: a 70 kg person has 70 kg of mass on Earth, the Moon, or the International Space Station. Weight is the force gravity exerts on that mass — on the Moon (1/6 Earth gravity), the same person weighs only 11.7 kg-force. This distinction affects calibration of scales: a spring scale measures weight (force) and gives different readings at different altitudes, while a balance scale compares masses and works identically everywhere. For precision applications like pharmaceutical compounding, laboratory work, and gemstone trading, instruments must be calibrated for local gravitational acceleration, which varies from 9.764 to 9.834 m/s² across Earth's surface — enough to create measurable discrepancies on analytical balances reading to 0.001 grams.
English-speaking countries historically used three different pound systems simultaneously. The avoirdupois pound (16 ounces, 453.592 grams) is the standard for general commerce — when a recipe says "one pound of butter," this is the system. The troy pound (12 troy ounces, 373.242 grams) is used exclusively for precious metals and gemstones: a troy ounce is 31.103 grams versus 28.350 grams for a standard (avoirdupois) ounce. This means a "pound" of gold (373g) actually weighs less than a "pound" of feathers (454g), despite the famous riddle implying they're the same. The apothecary system, once used by pharmacists, measured in grains (64.799 mg), scruples (20 grains), drams (3 scruples), and ounces (8 drams). Modern pharmacy has fully converted to metric, but you may encounter grain measurements on older medication dosages — aspirin was traditionally dosed at 5 grains (325 mg).
In logistics, the billable weight of a shipment is not always its actual weight. Carriers calculate dimensional weight (also called volumetric weight) by multiplying length × width × height and dividing by a dimensional factor — typically 5,000 for metric measurements (cm/kg) or 139 for imperial (inches/lbs). The carrier charges whichever is higher: actual weight or dimensional weight. A large, lightweight package (like a box of pillows measuring 60×50×40 cm weighing 5 kg) has a dimensional weight of 24 kg — nearly five times its actual weight — and is billed accordingly. This system exists because cargo planes and trucks run out of space before they run out of weight capacity with lightweight goods. Understanding dimensional weight explains why shipping costs for bulky items seem disproportionately high and why compact packaging saves real money: reducing a box from 60×50×40 to 50×40×30 cm cuts dimensional weight from 24 kg to 12 kg, potentially halving shipping costs while the actual contents haven't changed at all.
In everyday language, weight and mass are interchangeable — but in science, engineering, and international trade, the distinction matters. Mass measures the amount of matter in an object and doesn't change with location: a 70 kg person has 70 kg of mass on Earth, the Moon, or the International Space Station. Weight is the force gravity exerts on that mass — on the Moon (1/6 Earth gravity), the same person weighs only 11.7 kg-force. This distinction affects calibration of scales: a spring scale measures weight (force) and gives different readings at different altitudes, while a balance scale compares masses and works identically everywhere. For precision applications like pharmaceutical compounding, laboratory work, and gemstone trading, instruments must be calibrated for local gravitational acceleration, which varies from 9.764 to 9.834 m/s² across Earth's surface — enough to create measurable discrepancies on analytical balances reading to 0.001 grams.
English-speaking countries historically used three different pound systems simultaneously. The avoirdupois pound (16 ounces, 453.592 grams) is the standard for general commerce — when a recipe says "one pound of butter," this is the system. The troy pound (12 troy ounces, 373.242 grams) is used exclusively for precious metals and gemstones: a troy ounce is 31.103 grams versus 28.350 grams for a standard (avoirdupois) ounce. This means a "pound" of gold (373g) actually weighs less than a "pound" of feathers (454g), despite the famous riddle implying they're the same. The apothecary system, once used by pharmacists, measured in grains (64.799 mg), scruples (20 grains), drams (3 scruples), and ounces (8 drams). Modern pharmacy has fully converted to metric, but you may encounter grain measurements on older medication dosages — aspirin was traditionally dosed at 5 grains (325 mg).
In logistics, the billable weight of a shipment is not always its actual weight. Carriers calculate dimensional weight (also called volumetric weight) by multiplying length × width × height and dividing by a dimensional factor — typically 5,000 for metric measurements (cm/kg) or 139 for imperial (inches/lbs). The carrier charges whichever is higher: actual weight or dimensional weight. A large, lightweight package (like a box of pillows measuring 60×50×40 cm weighing 5 kg) has a dimensional weight of 24 kg — nearly five times its actual weight — and is billed accordingly. This system exists because cargo planes and trucks run out of space before they run out of weight capacity with lightweight goods. Understanding dimensional weight explains why shipping costs for bulky items seem disproportionately high and why compact packaging saves real money: reducing a box from 60×50×40 to 50×40×30 cm cuts dimensional weight from 24 kg to 12 kg, potentially halving shipping costs while the actual contents haven't changed at all.
→ Quick lb→kg: Divide by 2.2.
→ For cooking: 1 oz ≈ 28 g is accurate enough.
→ For precious metals: Use troy ounces (31.1 g), not avoirdupois.
→ For shipping: Check dimensional weight too — not just actual weight.
See also: Temperature · Length · Volume · BMI