Weight & Mass Converter: kg, lb, oz, g, stone, tons and troy units

How it works

kilograms = value × (kg per FROM unit) · result = kilograms ÷ (kg per TO unit) · combined factor = kg per FROM ÷ kg per TO · 1 lb = 0.45359237 kg (exact) · 1 oz = 1/16 lb = 28.349523125 g · 1 st = 14 lb · 1 grain = 64.79891 mg · 1 troy oz = 480 grains = 31.1034768 g

Every conversion goes through the kilogram. The value is multiplied by the number of kilograms in the starting unit and then divided by the number of kilograms in the target unit, so any pair of the 18 units can be converted with the same two steps. The factors are the legal definitions, not rounded approximations: since 1959 the international avoirdupois pound is exactly 0.45359237 kg, and the ounce (1/16 lb), dram (1/256 lb), stone (14 lb), US hundredweight (100 lb), UK hundredweight (112 lb), US short ton (2,000 lb) and UK long ton (2,240 lb) all follow from it. The grain is exactly 64.79891 mg and is shared by both systems; the troy ounce is 480 grains (31.1034768 g), the pennyweight 24 grains and the troy pound 12 troy ounces. The metric carat is 200 mg. Besides the main result the converter shows the conversion factor in both directions, the same mass in every unit, a quick table for common amounts and, for everyday amounts, the mass split into pounds and ounces and into stone and pounds (the way body weight is given in the UK and Ireland). Choose fewer significant figures under More options when you want a rounded answer. Strictly, these are units of mass. Weight is the force of gravity on a mass, and it changes slightly with location, but on Earth scales and labels use mass units, so the words are used interchangeably.

Worked example

Convert 1 pound to kilograms: kg = 1 × 0.45359237 = 0.45359237 kg, and the reverse factor is 1 kg = 1 ÷ 0.45359237 = 2.204622622 lb. The same pound is 16 oz, 453.59237 g or 7,000 grains. Because 1 lb is less than one stone (14 lb), no stone breakdown is shown; a 72 kg person, by contrast, weighs 72 ÷ 0.45359237 = 158.73 lb, which is 11 st 4.7 lb.

Sources: NIST: Unit conversion and SI references (HB 44 Appendix C, SP 811) · Wikipedia: Grain (unit), exactly 64.79891 mg · Wikipedia: Stone (unit), 14 lb · CalculatorSoup: weight and mass conversion factors

Frequently asked questions