Weight Converter

There is nothing to install and no convert button; the answer follows whatever you type.

1. Enter the amount in the Value box. Decimals such as 2.5 are accepted.
2. Choose the unit you have in From, for example Pound (lb), and the unit you want in To, for example Kilogram (kg).
3. Read the large result and the line beneath it, which shows the factor for one unit in both directions.
4. Press Swap units to check the conversion the other way round.
5. Scan the In every unit list for the same weight in all nine units, from milligrams to UK tons.

The display rounds to four decimals between 1 and 1,000, two decimals above that and six below 1. Everything is worked out in your browser, so nothing you enter leaves your device.

Imperial and US units are defined by agreement against the kilogram, so the converter can use exact values rather than approximations. Each unit is stored as its mass in kilograms, and every conversion passes through that one base.

• 1 pound = 0.45359237 kg exactly, and 1 kg is about 2.2046 lb
• 1 ounce = 1/16 pound = 28.349523125 g
• 1 stone = 14 pounds = 6.35029318 kg
• 1 US ton (short ton) = 2,000 pounds = 907.18474 kg
• 1 UK ton (long ton) = 2,240 pounds = 1,016.0469088 kg
• 1 metric tonne = 1,000 kg, 1 kg = 1,000 g and 1 g = 1,000 mg

The ounce here is the avoirdupois ounce used for food and body weight. The troy ounce of about 31.1035 g, used for gold, silver and platinum, is not in the list, so do not use this tool for bullion prices. There is also no combined stone-and-pounds field: stone appears as a decimal.

Try these values to check the tool against your own sums.

• 150 lb is 68.0389 kg, and 70 kg is 154.3236 lb.
• 23 kg is 50.7063 lb, a figure worth knowing for a checked baggage allowance, and 8 lb is 3.6287 kg, the kind of figure on a newborn record.
• 500 g is 17.637 oz or 1.1023 lb, and 100 g is 3.5274 oz.
• 1 tonne is 1.1023 US tons or 0.9842 UK tons.
• 10 stone is 63.5029 kg.

Stone needs one extra step. 70 kg converts to 11.0231 st. The whole number is 11 stone, and the 0.0231 stone left over times 14 is about 0.32 lb, so 70 kg is 11 st 0.3 lb. To go the other way, change stone and pounds into pounds first. A weight of 12 st 7 lb is 12 times 14 plus 7, which is 175 lb, and typing 175 into the converter with Pound (lb) selected gives 79.3787 kg. Typing 12.7 as stone would be wrong, since 12.7 st is 12 st 9.8 lb.

In physics, kilograms and pounds measure mass, the amount of matter, while weight is the force of gravity on that mass. On Earth the two move together, so everyday usage treats them as the same and so does this converter. The same 70 kg person would weigh less on the Moon but would still have a mass of 70 kg.

Most errors come from the units. People confuse the US ton, the UK ton and the metric tonne, which differ by up to about 12 percent, so check which one a shipping document means. Another is converting between weight and volume: a cup of flour and a cup of water have different masses, so for liquids in recipes the volume converter is the right tool, but a dry ingredient needs a weight on the scale. A third is rounding too early. Keep the full figure until the final step, then round. Remember too that the display rounds to four decimals, so a long exact value such as 68.0388555 appears as 68.0389, and use the exact definitions above if you need more digits for a calculation of your own.

Once you have a weight in kilograms, the BMI calculator and ideal weight calculator take it with a height from the length converter, and the calorie calculator also accepts pounds directly.