Stones to kilograms

Stone persists almost exclusively in UK body-weight conversation: on bathroom scales, at the doctor's office, and in everyday talk about weight. One stone is exactly 14 pounds, or about 6.35 kilograms, a figure worth knowing since stone rarely appears alongside a metric weight on the same scale or medical form, so a UK-reported weight often needs converting before it can be compared against international health guidance, a fitness app, or a weighing machine bought outside the UK.

British horse racing adds a second, more specialized use: jockeys and the weight a horse carries are given in stone and pounds, such as 9 stone 7, meaning 9 stone plus 7 pounds. Converting those racing weights to kilograms is necessary for comparing against international racing bodies or sports-science equipment that works exclusively in metric units, and it matters just as much for a jockey monitoring their own weight against a strict riding limit set in either unit.

A stone is simply 14 pounds bundled into one unit, so it converts to kilograms with a single fixed multiplier inherited from the pound-to-kilogram relationship.

Multiply the stone value by 6.35029318 to get kilograms:

kg = st × 6.35029318

At common body-weight figures: 10 stone comes to 63.503 kg, 12 stone comes to 76.204 kg, and 15 stone comes to 95.254 kg, giving a useful spread of reference points across a typical adult weight range.

For body weight, two decimal places (63.50 kg) is more than enough precision; rounding to a whole kilogram is fine for casual conversation, since body weight naturally fluctuates by more than that from one day to the next.

The most common mistake is treating a weight written as stone and pounds, like 11 stone 4, as the decimal 11.4 stone. It is not: the 4 means 4 pounds, so the correct total is 11 stone (69.853 kg) plus 4 pounds (1.814 kg), for 71.667 kg, noticeably different from the 72.393 kg a naive 11.4 × 6.35029318 calculation would give, an error of over half a kilogram.