The exact conversion
One stone is exactly 14 pounds, which is exactly 6.35029 kilograms. So stone to kg multiplies by 6.35, kg to stone divides by 6.35, and the pounds remainder is whatever is left after the whole stones. Example: 80 kg divided by 6.35029 is 12.598 stone; the 0.598 times 14 gives 8.4 pounds, so 80 kg reads as 12 st 8 lb on a UK scale.
Quick reference chart
| Stone | Kilograms | Pounds |
|---|---|---|
| 8 st | 50.8 kg | 112 lb |
| 9 st | 57.2 kg | 126 lb |
| 10 st | 63.5 kg | 140 lb |
| 11 st | 69.9 kg | 154 lb |
| 12 st | 76.2 kg | 168 lb |
| 13 st | 82.6 kg | 182 lb |
| 14 st | 88.9 kg | 196 lb |
| 15 st | 95.3 kg | 210 lb |
| 16 st | 101.6 kg | 224 lb |
| 18 st | 114.3 kg | 252 lb |
| 20 st | 127.0 kg | 280 lb |
Why does the UK weigh people in stone?
The stone survives from medieval trade, where goods were weighed against literal stones standardized by market. Britain fixed it at 14 pounds in 1835, and although the UK went metric for commerce in 1985, body weight in conversation, in doctors offices and on bathroom scales stayed in stone and pounds. Ireland uses it too; the US skipped it entirely and uses pounds alone, which is why a 12 st 8 lb Brit and a 176 lb American weigh exactly the same and understand each other not at all.
Reading a stone and pounds weight
The format 11 st 4 lb means 11 whole stones plus 4 pounds: 11 x 14 + 4 = 158 lb, or 71.7 kg. Half a stone is 7 lb. Losing a stone means losing 14 lb or 6.35 kg. If you are tracking weight loss across unit systems, convert once at the start and the end rather than every weigh in, since rounding each conversion adds noise to the trend. This converter is unrelated to rock and gravel by weight; for those, use the stone calculator for landscaping material.