Mass Conversion Calculator

1 kg is about ≈ 2.20462 lb, and 1 lb is exactly 0.45359237 kg

Every mass unit is tied back to the gram. The international pound is defined as exactly 0.45359237 kg, so pounds to kilograms gives an exact answer with no rounding, while kilograms to pounds never terminates: 1 kg ≈ 2.20462262 lb. An ounce is 1/16 lb, so 1 oz = 28.349523125 g, and a stone is 14 lb, so 1 st = 6.35029318 kg. For the questions people search most: 70 kg ≈ 154.324 lb, or about 11 st 0.3 lb, and 10 stone is 140 lb, which is 63.5029318 kg.

The trap in mass conversion is that one name often covers several sizes. The troy ounce that gold is priced in is 31.1034768 g, heavier than the everyday ounce. A US ton is 2,000 lb, a UK ton is 2,240 lb and a metric tonne is 1,000 kg. A "catty" or "jin" can be 500 g, 600 g or about 605 g depending on the place. The calculator above gathers these in its "Same name, different weight" tabs, and you can type into either pan: the other pan always shows the same mass.

How to use the calculator

1. Type a number into the left pan or the right pan and choose its unit under "Unit". The other pan shows the same mass in the unit you picked for it. If you edit the other pan instead, that pan becomes the source.
2. You can enter decimals such as 2.5, fractions such as 1 1/2, or exponents such as 1.6e-27 or 1.6 × 10^-27. A comma is read as a thousands separator only when it sits after every three digits, so 1,000 means one thousand.
3. Choose "Pounds + ounces" or "Stone + pounds" as the unit and that pan splits into two boxes. Use it for values written in two units, such as a newborn at 7 lb 8 oz or an adult at 10 st 5 lb, either to enter them or to read a result in that form.
4. The swap button (⇄) between the pans exchanges their units and values. The mass stays the same, and a value you typed keeps all its digits.
5. The balance picture shows the same mass as weights on both pans. The weights come in groups of 1, 2, 2 and 5, and their size follows the cube root of the mass. When the value changes, the balance tips for a moment and then levels again.
6. Under "Same name, different weight", pick a family such as ounce, pound, ton, jin or liang to see its sizes as bars. Tapping a bar, or an entry under "All units", makes it the unit of the other pan. "Find a unit" accepts names, symbols and Chinese or Japanese characters.
7. Choose 4, 6 or 10 significant digits. "Copy result" copies both pans as one line, and "Copy link" copies an address that restores the current state.

How the conversion works: everything goes through grams

The calculator multiplies your value by the grams in one unit of its type, then divides by the grams in one unit of the target. Converting 1 kg to pounds is 1,000 g ÷ 453.59237 g ≈ 2.20462 lb, and 10 stone to kilograms is 140 lb × 453.59237 g = 63,502.9318 g. Unit sizes are defined values, so they are kept as exact fractions and rounded only for display. A rounded result is marked with "≈".

• Pound, ounce, grain: the UK Weights and Measures Act 1985 (Schedule 1) sets the pound at 0.45359237 kg, and NIST uses the same value. A pound is 16 oz and 7,000 gr, which makes 1 gr = 64.79891 mg exactly.
• Troy and apothecaries’ units: the troy ounce is 480 gr = 31.1034768 g, and 12 troy ounces make a troy pound. A pennyweight is 24 gr, an apothecaries’ scruple 20 gr and an apothecaries’ dram 60 gr.
• Tonne and carat: the metric tonne is 1,000 kg, and the metric carat is exactly 200 mg (NIST SP 811).
• Asian units: Hong Kong, mainland China, Taiwan, Korea, Japan, India and Indonesia each have their own definitions. They are compared in the section on Asian units below.
• Particle masses: the dalton, electron, proton, neutron and Planck masses are measured values, so the calculator uses the CODATA 2022 recommended values.

kg to lb and lb to kg: common conversions

To go from kilograms to pounds, multiply by about 2.20462. To go from pounds to kilograms, multiply by 0.45359237. As a quick estimate, multiply kilograms by 2.2: that is only about 0.46 lb off at 100 kg (2.2 × 100 = 220 lb against 220.462 lb).

Weights given in pounds and ounces, such as a baby’s birth weight, convert by turning the ounces into a fraction of a pound first. Eight ounces is half a pound, so 7 lb 8 oz is 7.5 lb, which is 3.401942775 kg, or ≈ 3.402 kg to four digits.

US nutrition labels round 1 oz to 28 g for labelling (21 CFR 101.9). The exact value is 28.349523125 g, so a gram figure on a label can differ slightly from the calculator.

Stones and pounds: body weight in the UK and Ireland

A stone is 14 lb, which is 6.35029318 kg. The stone remains in customary use for body weight in the United Kingdom and Ireland, and in sports such as boxing and horse racing, while Australia and New Zealand have replaced stones and pounds with kilograms since the 1970s (Wikipedia, "Stone (unit)"). To turn a weight in kilograms into stones and pounds, divide by 6.35029318, keep the whole number as stones, and multiply the remainder by 14 to get pounds. Choosing "Stone + pounds" as the unit does this for you.

Going the other way, 10 stone is 140 lb, so 10 stone is 63.5029318 kg. A weight of 10 st 5 lb is 145 lb, which is about 65.7709 kg. The table below lists whole stones.

Why stones? The word comes from the old practice of using stones as weights. The Wikipedia article on the unit says that Edward III set the stone at 14 pounds for wool and other merchandise in 1350, and that Henry VII reaffirmed it in 1495. The 1985 Act lists the stone as 14 lb, and it is still how many people in Britain and Ireland say their own weight.

Tons and hundredweights: US, UK and metric

The word "ton" covers three different masses. The US short ton is 2,000 lb, the UK long ton is 2,240 lb, and the metric tonne is 1,000 kg. A hundredweight also differs: 100 lb in the US and 112 lb in the UK, so a ton is 20 hundredweights in both systems. When a shipping or commodity report says "ton", check which one it means before converting.

NIST SP 811 gives the same sizes rounded: 907.1847 kg for the short ton and 1,016.047 kg for the long ton. The calculator keeps the exact fractions.

Troy ounces, grains and gold

Gold, silver and platinum prices are normally quoted per troy ounce, which is 31.1034768 g. The everyday (avoirdupois) ounce used for food and parcels is 28.349523125 g, so a troy ounce is about 9.7% heavier. Dividing a gold price per troy ounce by 28.35 instead of 31.1035 therefore overstates the price per gram by that much. A troy pound is also different: it is 12 troy ounces, or 373.2417216 g, which is lighter than the 16-ounce pound of 453.59237 g.

The grain ties these systems together. One grain is 1/7,000 lb = 64.79891 mg exactly, and it is the same grain in the everyday, troy and apothecaries’ systems. An everyday ounce is 437.5 gr, a troy ounce is 480 gr, a pennyweight is 24 gr (1.55517384 g), and a metric carat for gemstones is 200 mg, about 3.08647 gr. The "K" in 18K gold is a purity grade, not the carat of mass. The Indian tola, used for gold in South Asia, is 11.6638038 g, which is exactly 0.375 troy ounce.

Catty, tael and tola: Asian units in brief

Jin (斤, catty) and liang (兩, tael) are used across East and Southeast Asia, and the same name does not mean the same weight. Mainland China moved from 16 liang to 10 liang per jin by a State Council order in 1959, which put 1 kg at 2 shì jīn. Hong Kong law defines the catty as 0.60478982 kg, with the tael as 1/16 catty and the picul as 100 catties. Taiwan’s 台斤 is 600 g.

The Japanese momme is 3.75 g, and Japan’s Measurement Unit Order still allows it for weighing pearls. In Indonesia an ons is 100 g (KBBI), not the 28.35 g ounce, and a kati is 6¼ ons. All of these are in the calculator’s groups for China, Japan and South and Southeast Asia.

Common mistakes

• Using the everyday ounce for gold: gold prices are per troy ounce (31.1034768 g). Using 28.35 g makes the price per gram about 9.7% too high.
• Treating fluid ounces as ounces of mass: a fluid ounce measures volume. A US fluid ounce of water weighs close to an ounce, but honey or oil does not.
• Mixing up the three tons: 2,000 lb, 2,240 lb and 1,000 kg are different. 1,000 UK tons exceed 1,000 US tons by about 109 tonnes.
• Reading a decimal stone as pounds: 11.5 st is 11 st 7 lb, not 11 st 5 lb. Multiply the part after the point by 14.
• Confusing carat and karat: a gemstone’s carat is 200 mg, while the K in 18K or 24K gold describes purity.
• Reading ons as ounce: an Indonesian ons is 100 g, about 3.5 times an ounce.

Limits and cautions

• This tool converts between mass units using defined factors and CODATA 2022 recommended values. It does not account for gravity or air buoyancy, and it does not convert to force units such as newtons, kilogram-force or pound-force. At standard gravity 1 kgf is 9.80665 N.
• Particle masses are measured values with an uncertainty. The calculator treats the recommended value as exact, so the last digit of a result does not show measurement precision.
• The Asian units follow the reference values above. Historical or regional jin, liang and similar units can differ.
• Values from 0 to 10 to the power of 30 are accepted. Results below 10⁻⁶ or from 10¹⁵ upward are shown in "× 10ⁿ" form.
• For trade, medicine or lab work, use a certified scale and the units your jurisdiction requires. This page converts figures; it does not make a scale more accurate.

Standards checked on 21 October 2026: the UK Weights and Measures Act 1985, NIST SP 811 Appendix B.8, CODATA 2022 and the sources listed below.

Sources

• 01legislation.gov.uk — Weights and Measures Act 1985, Schedule 1pound 0.453 592 37 kg, stone 14 lb, hundredweight 112 lb, ton 2240 lb, ounce troy 0.031 103 476 8 kg
• 02NIST SP 811 Appendix B.8 — Factors for units listed alphabeticallygrain 64.798 91 mg and carat (metric) 200 mg (exact), short ton 907.184 7 kg, long ton 1 016.047 kg, slug 14.593 90 kg
• 03NIST — CODATA internationally recommended 2022 values of the fundamental physical constantsatomic mass constant 1.660 539 068 92(52) × 10⁻²⁷ kg, electron, proton, neutron and Planck masses
• 04Wikipedia — Stone (unit)customary use for body weight in the UK and Ireland; 14-pound stone for wool in 1350 (Edward III), reaffirmed 1495
• 05Hong Kong e-Legislation — Weights and Measures Ordinance (Cap. 68)1 catty = 0.604 789 82 kg, 1 tael = 1/16 catty, 1 picul = 100 catties
• 06State Council Gazette 1959 — Order on unifying China’s system of weights and measures16 liang per jin changed to 10 liang per jin; 1 kg = 2 shì jīn
• 07Legislative Yuan, Taiwan — reference document台斤 = 600 g, 台兩 = 37.5 g
• 08e-Gov Law Search — Measurement Unit Order (計量単位令)pearl mass in momme (もんめ) = 0.00375 kg
• 09The Standards of Weights and Measures Act, 1976 (India, copy)1 tola = 0.011 663 803 8 kilogram
• 10KBBI (Indonesian dictionary) — ons, kations: seratus gram (100 g); kati: 6¼ ons
• 11eCFR — 21 CFR 101.9 Nutrition labeling of food(b)(5)(viii): 1 oz = 28 g on nutrition labels
• 12Standard Korean Language Dictionary — dona don is 1/10 nyang and 10 pun, 3.75 g; the dictionary entry for gwan (word_no=398758) gives 3.75 kg, and geun 600 g (meat, herbs) or 375 g (fruit, vegetables)

Frequently asked questions

Related tools