Mass and weight in everyday use
In daily life people say "weight" when they strictly mean mass: how much matter an object contains. Scientists distinguish the two, since weight is the force of gravity on a mass, but every unit in this converter measures mass, and the conversion is the same whichever word you use. The metric system is built on the kilogram, and the pound used in the United States and United Kingdom is defined from it, exactly 0.45359237 kilograms since the 1959 international agreement.
How the converter calculates
Each unit is stored as a multiple of one kilogram. Your value is multiplied into kilograms and then divided by the size of the target unit. For 70 kg to pounds that is 70 ÷ 0.45359237 = 154.324 lb. Since the factors are exact definitions, converting from pounds to kilograms and back returns the number you started with, apart from the display rounding.
Handy reference values
- 1 kilogram = 2.20462 pounds = 35.274 ounces.
- 1 pound = 16 ounces = 453.592 grams.
- 1 stone = 14 pounds = 6.35029 kilograms. Stone is still used for body weight in the UK and Ireland.
- 1 metric tonne = 1,000 kilograms, while one US short ton is 2,000 pounds, about 907.18 kilograms.
Where people use it
Common jobs include converting body weight for a fitness plan, working out whether a bag fits an airline limit (often 23 kg, or about 50.7 lb), scaling recipes between grams and ounces, and checking the weight of parcels for international shipping. For cooking, remember that ounces here are mass ounces. Fluid ounces measure volume, and a fluid ounce of water weighs about 29.6 grams, but a fluid ounce of honey weighs more. Use the volume converter for liquids measured in cups or millilitres.
Avoiding mistakes
Watch out for the three different "tons": the metric tonne (1,000 kg), the US short ton (2,000 lb) and the UK long ton (2,240 lb). This tool includes the first two; if a document says only "ton", check which country it comes from. When entering stone and pounds, such as 11 st 4 lb, convert the stone to pounds first (11 × 14 = 154), add the pounds, and then enter 158 as pounds. All calculations happen locally in your browser, so nothing you enter is stored or sent.