Convert stones to kilograms

The formula

kilograms = stones × 6.3502932

stones to kilograms — quick reference

Six and a third kilos to the stone, plus whatever the pounds add

A stone is 6.35 kg, so multiplying the stones by six and adding a third of that same number lands very close: eleven stone is 66 plus 3.7, or 69.7 kg, against a true 69.85. The fixed points are easier still - 10 stone is 63.5 kg, 12 stone is 76.2, 14 stone is 88.9.

The pounds are a separate sum, at roughly 0.45 kg each. Eleven stone four is 69.85 plus 1.81, or 71.7 kg. What cannot be done is treating the pounds as a decimal: entering 11.4 gives 72.4 kg, close enough to look right and wrong enough to matter.

Every clinical number downstream of this one is metric

BMI is kilograms divided by height in metres squared, and doses are written in milligrams per kilogram - anaesthetic agents, chemotherapy, paediatric antibiotics and contrast media all scale with body mass. A stone figure cannot enter any of those calculations, which is why UK medical forms ask for kilograms even from patients who have never once weighed themselves in them.

Rounding tolerance differs by purpose. To the nearest kilogram is fine for a BMI, where the categories are wide; it is not fine for a small child, where one kilogram can shift a dose by several per cent. And outside Britain and Ireland, a form will not offer a stones field at all.

Questions