Convert Stones to Kilograms

The UK's Unique Weight Unit

One stone equals exactly 6.35029318 kilograms, or 14 pounds. The stone is used almost exclusively in the United Kingdom and Ireland for body weight. Walk into a doctor's office in London and they will likely record your weight in stones and pounds. Walk into one in Paris, Berlin, or New York and nobody will know what you mean.

This unit persists in British culture despite the UK beginning its transition to metric in the 1960s. Personal scales sold in Britain still offer a stone display mode. Weight loss programs in the UK celebrate "dropping a stone" the way Americans celebrate "losing 10 pounds."

Body Weight Conversion Table

The Math is Straightforward

Multiply stones by 6.35 for kilograms. For stones-and-pounds (like "11 stone 7"), convert the extra pounds separately: 11 x 6.35 = 69.85 kg, plus 7 lbs x 0.4536 = 3.175 kg, total 73.0 kg.

A faster shortcut: multiply by 6.35, or for rough estimates, multiply by 6 and add half a stone's worth (about 3 kg). So 12 stone is roughly 72 + 3.8 = 75.8 kg (actual: 76.2 kg).

Why 14 Pounds?

The stone's definition as 14 pounds dates to the medieval English wool trade. Merchants needed a standard weight for pricing wool, and 14 pounds became the legal standard under Edward III in 1350. Different commodities actually used different stone weights for centuries. A stone of glass was 5 pounds, a stone of lead was 12 pounds. Parliament legally defined the stone as 14 pounds for trade in the Weights and Measures Act of 1835, though regional variations persisted for decades.

Medical Records and the Stone Problem

If you move from the UK to a country using metric, your medical history might list weights in stones. Most international doctors need kilograms. BMI calculators require metric input. Knowing your weight in kilograms is worth memorizing for medical forms, fitness tracking apps, and medication dosing, where "10 mg per kilogram of body weight" requires actual kilograms, not stones.