Weight Calculator
Press Calculate to see the results.
Enter an amount and pick two units to convert between. This weight calculator covers metric, US and imperial units, from milligrams and carats to stone and tons, and shows the same amount in every other unit.
In everyday speech, weight means how heavy something is, and that is how the units in this converter are used: a kilogram or a pound tells you how much matter an object contains. Strictly speaking those are units of mass, and physicists reserve the word weight for the force gravity exerts on that mass. On Earth's surface the two are proportional, so for shopping, cooking, shipping and health the difference does not matter.
Common Weight
The table gives a sense of scale, from subatomic particles to the Sun. Particle masses are recommended values from the CODATA committee of the International Science Council; astronomical masses are rounded.
| Object | Approximate mass |
|---|---|
| Sun | 1.989 × 10³⁰ kg (about 333,000 Earths) |
| Earth | 5.972 × 10²⁴ kg |
| Moon | 7.342 × 10²² kg (about 1.2% of Earth) |
| Blue whale (adult) | 100,000 – 150,000 kg |
| African elephant (adult male) | about 6,000 kg |
| Midsize car | about 1,500 kg (3,300 lb) |
| US nickel coin | 5 g |
| Atomic mass unit (u) | 1.66053907 × 10⁻²⁷ kg |
| Neutron | 1.67492750 × 10⁻²⁷ kg (1.00866 u) |
| Proton | 1.67262192 × 10⁻²⁷ kg (1.00728 u) |
| Electron | 9.1093837 × 10⁻³¹ kg (0.000549 u) |
Why We Have Different Ways to Measure Weight?
People weighed things long before anyone agreed on how. Early units were based on whatever was at hand: seeds, stones and coins. The grain, still used for bullets, arrows and medicines, was originally the weight of a single grain of barley or wheat. The carat used for gemstones comes from the carob seed, once thought to be unusually uniform in weight; it was standardized in 1907 at exactly 200 milligrams. The stone, literally a stone kept as a reference weight, varied from town to town and from one trade to another before England settled on 14 pounds.
Trade pushed communities toward common standards, because buyers and sellers needed to trust a market's scales. Rulers kept official weights and punished merchants who cheated, yet each kingdom, and often each trade, had its own. England by the late Middle Ages used troy weight for precious metals, apothecaries' weight for medicines and avoirdupois weight for everything else, with different ounces in each.
The metric system, introduced in France in the 1790s, tried to end the confusion with one decimal system tied to nature: the gram was the mass of one cubic centimeter of water. It is now used officially almost everywhere. The United States still uses customary pounds and ounces in daily life, though since 1893 they have been defined in metric terms, and the United Kingdom uses kilograms in shops while many people still give their body weight in stone and pounds.
Specialized units survive because they suit their fields. Jewelers price diamonds in carats and points, chemists use the atomic mass unit to compare atoms, pharmacists once used grains, and shipping and mining use tonnes. Converting between them is a matter of multiplying by fixed factors, all of which are now defined exactly in kilograms.
The US and UK versions of some units differ. A US quarter is a quarter of a 100-pound short hundredweight, or 25 pounds, while a UK quarter is a quarter of the 112-pound long hundredweight, or 28 pounds. The table lists the definitions this converter uses.
| Unit | Definition | In kilograms |
|---|---|---|
| Pound (lb) | International avoirdupois pound | 0.45359237 |
| Ounce (oz) | 1/16 pound | 0.028349523125 |
| Grain (gr) | 1/7,000 pound | 0.00006479891 |
| Carat (ct) | 200 milligrams | 0.0002 |
| Stone [UK] | 14 pounds | 6.35029318 |
| Stone [US] | 12.5 pounds | 5.669904625 |
| Quarter [UK] | 28 pounds | 12.70058636 |
| Quarter [US] | 25 pounds | 11.33980925 |
| Ton (metric) | 1,000 kilograms | 1,000 |
Frequently asked questions
How many kilograms is one pound?
One pound is exactly 0.45359237 kilograms, or about 0.454 kg. To convert pounds to kilograms, multiply by 0.4536; to go from kilograms to pounds, multiply by 2.2046.
How many pounds are in a stone?
A UK stone is 14 pounds (about 6.35 kg). Someone weighing 11 stone 6 pounds weighs 160 pounds.
How many ounces are in a pound?
There are 16 avoirdupois ounces in a pound. Troy ounces, used for gold and silver, are about 10% heavier, and there are 12 of them in a troy pound.
What is the difference between weight and mass?
Mass is the amount of matter in an object and is the same everywhere. Weight is the force of gravity on that mass, so it changes on the Moon or other planets. Everyday units like pounds and kilograms measure mass.
Updated by Calculator.hair. How we build and check our calculators