Kilograms to Stone

The stone is an old English unit of 14 avoirdupois pounds. Medieval markets used stones of different sizes for wool, meat and other goods, but the 14 lb stone became the standard, and since the 1959 international pound of 0.45359237 kg it has been exactly 6.35029318 kg. It is no longer used for trade, yet in the UK and Ireland it survives as the everyday way to talk about body weight.

That is why a British doctor may record your weight in kilograms while you describe it as eleven stone four. Boxing, horse racing and slimming clubs in Britain still quote stone and pounds, and bathroom scales sold there usually switch between kg, st and lb.

People rarely say 11.02 st. They say 11 stone and the leftover pounds, so a kilograms result needs one more step: take the whole stone, multiply the decimal part by 14, and that is the pounds. 80 kg is 12.598 st, which is 12 st plus 0.598 × 14 = 8.4 lb, or 12 st 8 lb. 100 kg works out at 15 st 10.5 lb.

Note the British plural: the unit is normally written as stone even for many of them, as in a 12 stone man. The symbol is st.

A decimal stone is not stone and pounds. 11.5 st means eleven and a half stone, which is 11 st 7 lb, not 11 st 5 lb, because half of 14 is 7. Reading the decimal as pounds understates the weight. The reverse question is answered on the stone to kilograms page, and plain pounds are on kilograms to pounds.

Rounding matters less than people think: one pound is only 0.45 kg, so a scale that reads to the nearest pound is fine for tracking weight over weeks.