Weight and Mass Converter

How it works

Every unit here is defined as an exact number of kilograms. The milligram and gram are a millionth and a thousandth of a kilogram, and the metric tonne is a thousand kilograms. Since the international yard and pound agreement of 1959 the avoirdupois pound has been defined as exactly 0.45359237 kg; the ounce is a sixteenth of a pound, the stone (still used for body weight in the UK and Ireland) is 14 pounds, the US short ton is 2,000 pounds and the UK long ton is 2,240 pounds.

The calculator multiplies your value by the size of the from unit in kilograms, then divides by the size of the to unit. The factor shown is what one from unit equals in the to unit.

Conversions within one system come out as whole numbers (16 ounces to the pound, 2,000 pounds to the ton). Pounds to kilograms is an exact decimal; kilograms to pounds is its reciprocal, 2.204623. Results are rounded to six decimal places for display only.

Formula

kilograms = value × kg per from unit
result    = kilograms ÷ kg per to unit
factor    = kg per from unit ÷ kg per to unit
1 lb = 0.45359237 kg   1 oz = 1/16 lb = 28.349523125 g   1 st = 14 lb = 6.35029318 kg   (exact)
1 ton = 2,000 lb = 907.18474 kg   1 long ton = 2,240 lb = 1,016.0469088 kg   1 t = 1,000 kg   1 mg = 0.001 g   (exact)

Example

The default, 1 pound to kilograms: 1 × 0.45359237 kg ÷ 1 kg = 0.453592 kg. The factor is 0.453592 kg per pound.

150 lb to kilograms is 150 × 0.45359237 = 68.038856 kg, or 150 ÷ 14 = 10.714286 stone (10 st 10 lb). 1 kg is 2.204623 lb, and a metric tonne is 2,204.622622 lb, about 10% more than a US short ton of 2,000 lb and 1.6% less than a UK long ton of 2,240 lb.

Assumptions and limitations

• Units use the exact legal definitions: the 1959 international yard and pound agreement (1 lb = 0.45359237 kg), the avoirdupois ounce, short ton and long ton (NIST Handbook 44, Appendix C), the stone of 14 lb (UK Weights and Measures Act 1985) and the SI (tonne = 1,000 kg, SI Brochure Table 8).
• Ounces and pounds are avoirdupois, the everyday weights. Troy ounces (31.1035 g, used for precious metals) and fluid ounces (a volume) are different units and are not included.
• Weight here means mass, as it does on a scale. The same mass weighs slightly less at the equator or at altitude, but all of these units convert by mass.
• A negative value converts with its sign kept, so a change in weight can be converted as well as a weight.
• Results are rounded to six decimal places for display; the arithmetic is done in full double precision.

Frequently asked questions