Weight and Mass Converter

How to use the weight converter

1. Type a number in Value, with a decimal point or a decimal comma (70.5 or 70,5).
2. Pick the starting unit in From and the target unit in To, for example kilogram to pound.
3. The result updates as you type. The line below it shows the complete conversion (“70 kg ≈ 154.32358 lb”) and Copy copies it.
4. Use the Swap units button (⇄) to reverse the conversion.
5. Change Significant figures to get a shorter or a more precise answer. A “≈” sign means the value shown has been rounded.

The tables under the result show your value in every unit, a quick conversion table for the selected pair, everyday reference weights (a sugar cube, a checked bag, a small car) and the definition of each unit in kilograms.

Exact definitions

The avoirdupois units used in the United States and the United Kingdom are defined from the kilogram:

• 1 pound (lb) = 0.45359237 kg exactly, since the 1959 international yard and pound agreement.
• 1 ounce (oz) = 1/16 lb = 28.349523125 g exactly.
• 1 stone (st) = 14 lb = 6.35029318 kg exactly. The stone is still common in the UK and Ireland for body weight.
• 1 tonne (t) = 1,000 kg, also called the metric ton.

Because the pound is an exact decimal, pounds to kilograms is a plain multiplication: 150 lb × 0.45359237 = 68.0388555 kg. The reverse, kilograms to pounds, divides by 0.45359237, which gives an endless decimal (1 kg ≈ 2.20462262 lb). The formula shown under the result is written in the exact form: lb = kg ÷ 0.45359237.

Weight or mass?

Strictly speaking, kilograms and pounds measure mass, the amount of matter in an object. Weight is the force of gravity on that mass and is measured in newtons. In everyday language, and on scales, “weight” means mass, and that is what this tool converts. The result does not depend on gravity: 1 kg is 2.2046 lb on Earth or on the Moon.

Examples

• Body weight: 70 kg ≈ 154.3 lb ≈ 11 st 0.3 lb (11.02 st).
• Cooking: 4 oz = 113.4 g; 250 g ≈ 8.82 oz; 1 lb ≈ 453.6 g.
• Luggage: a 23 kg checked bag limit is about 50.7 lb.
• Medicine: 500 mg = 0.5 g.

Not covered here: the troy ounce used for gold (31.1034768 g), the US short ton (2,000 lb) and the British long ton (2,240 lb). They differ from the ounce and the tonne listed above, so be careful when you see “ounce” on a bullion price or “ton” in a US document.