Stone Calculator: Convert Stones to Pounds and Kilograms
Free stone calculator: convert stones to pounds and kilograms, or pounds and kilograms back to stones, with the conversion steps shown.
What is a stone?
The stone (abbreviated st) is a unit of mass used chiefly in the United Kingdom and Ireland for measuring human body weight. One stone is defined as exactly 14 pounds, which equals 6.35029 kilograms. So a person who weighs 11 stone weighs 154 pounds, or about 69.9 kilograms. The unit dates back centuries to the wool trade, where stones of different sizes were used for different goods, but the 14-pound stone was standardized for everyday use and survives today mainly on bathroom scales and in conversation about weight.
This calculator converts in both directions: stones to pounds or kilograms, and pounds or kilograms back to stones. When converting back to stones, it gives the answer two ways, as a decimal (11.5 st) and broken into whole stones plus the leftover (11 st 7 lb), because that is how people actually say it: “eleven and a half stone.” Every conversion is a single multiplication or division by an exact factor, computed directly in your browser with the steps shown.
How to use the stone calculator
Type the weight into the first box, choose the conversion direction from the dropdown, and press Calculate. The four options cover every combination you are likely to need: stones to pounds (for understanding a UK weight in American terms), stones to kilograms (for medical or scientific contexts), and the reverse of each.
Weights cannot be negative, so the calculator rejects negative inputs. Decimals are welcome, half stones like 10.5 are completely normal in body-weight contexts. The kilogram factor 6.35029 is exact to five decimal places (14 × 0.45359237), which is far more precision than any bathroom scale can measure, so rounding is never a concern in practice.
The conversion formulas
All stone conversions rest on one definition: 1 st = 14 lb. The kilogram value follows from the international definition of the pound (1 lb = 0.45359237 kg exactly), giving 1 st = 14 × 0.45359237 = 6.35029 kg.
- Stones to pounds: multiply by 14. (11 st × 14 = 154 lb)
- Stones to kilograms: multiply by 6.35029. (11 st × 6.35029 = 69.85 kg)
- Pounds to stones: divide by 14. (154 lb ÷ 14 = 11 st)
- Kilograms to stones: divide by 6.35029. (70 kg ÷ 6.35029 ≈ 11.02 st)
To split a decimal stone figure into stones and pounds, take the whole number part as the stones and multiply the fractional part by 14 for the leftover pounds: 11.5 st = 11 st + (0.5 × 14) lb = 11 st 7 lb. The calculator does this breakdown automatically.
Example: convert 12 stone 6 pounds to kilograms
Step 1: Combine into stones: 6 lb ÷ 14 = 0.4286 st, so the total is 12.4286 st.
Step 2: Multiply by the factor: 12.4286 × 6.35029 = 78.93 kg.
Shortcut check: 12 st alone is 12 × 6.35029 = 76.2 kg, and 6 lb is 6 × 0.45359237 = 2.72 kg; 76.2 + 2.72 = 78.92 kg. Both routes agree.
More examples: 10 st = 140 lb = 63.5 kg; 200 lb = 14 st 4 lb; 80 kg = 12.6 st.
Common mistakes
- Confusing stones with pounds: 11 stone is not 11 pounds, it is 154 pounds. The numbers differ by a factor of 14, so always check which unit a figure is in before converting.
- Reading “11.5 stone” as “11 stone 5 pounds”: the .5 means half a stone, which is 7 pounds, so 11.5 st = 11 st 7 lb, not 11 st 5 lb.
- Rounding the kilogram factor too early: using 6.35 instead of 6.35029 introduces a small error that grows with larger weights. The calculator keeps full precision until the final display.
- Mixing stones into BMI-style formulas: formulas like body mass index expect kilograms (or pounds with a conversion constant), so convert stones to kg first rather than plugging stones in directly.
When the stone is used
The stone survives almost entirely as a body-weight unit in the UK and Ireland. Doctor’s offices may record kilograms, but patients still say “I want to get down to twelve stone.” It appears in boxing and wrestling weigh-ins, in historical recipes and literature, and anywhere British customary units persist. If you are tracking weight loss against a UK-based plan, converting your scale readings (usually kg or lb) into stones makes the targets feel concrete. For general unit conversions beyond weight, the unit converter handles length, and the percentage calculator is handy for working out weight change as a percentage.
Exactly 14 pounds. This is a definition, not a measurement, so there is no rounding involved: 10 stone is exactly 140 pounds.
6.35029 kg. It comes from 14 pounds × 0.45359237 kg per pound. For everyday purposes 6.35 kg is close enough, but the calculator uses the fuller figure.
It means 11 stone and 7 pounds, which is 11.5 stone or 161 pounds. When someone gives stones with a second number, that number is always pounds (0 to 13), never a decimal fraction.
Tradition and familiarity. The UK officially uses metric units, but stones remain the everyday language for body weight, much like feet and inches remain common for height. Medical records typically use kilograms.