The formula
st = kg × 0.1574730444
Where the factor comes from — each unit by its definition, then its size in SI:
1 kg is the SI unit of mass.1 st = 14 × lb = 6.35029318 kg
Dividing the two SI sizes gives the factor: 0.157473044418 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 6.35029318.
Physics formulas take mass in kilograms. Pounds (lb) are a unit of mass; pound-force (lbf) is the weight of a pound — a different quantity, on the force page.
Worked examples
- A family car: 1,500 kg = 236.21 st — 1,500 × 0.1574730444 = 236.21
- An adult: 75 kg = 11.8105 st — 75 × 0.1574730444 = 11.8105
- A bag of flour (1 lb): 0.453592 kg = 0.0714286 st — 0.453592 × 0.1574730444 = 0.0714286
- A block of butter (250 g): 0.25 kg = 0.0393683 st — 0.25 × 0.1574730444 = 0.0393683
Frequently asked questions
How many stone is 1 kg?
1 kg = 0.157473044418 st.
How do I convert stone back to kilograms?
Divide by 0.157473044418 — or multiply by 6.35029318: 1 st = 6.35029318 kg.