Stone to KG Converter

The formula

To convert stone to kilograms, multiply the stone value by the number of kilograms per stone:

kg = st × 6.35029

• kg — the result in kilograms.
• st — the input weight in stone.
• 6.35029 — the exact number of kilograms per stone (= 14 × 0.45359237 kg/lb = 6.35029318 kg), fixed by the 1959 International Yard and Pound Agreement.

If your weight includes remaining pounds (e.g. 11 st 9 lb), convert the pounds separately and add: kg = (st × 6.35029) + (lb × 0.45359).

Worked example

Using the calculator’s default input of 11 stone:

1. Take the stone value: 11.
2. Multiply by 6.35029: 11 × 6.35029 = 69.853.

So 11 stone ≈ 69.85 kg.

Stone to kg conversion chart

Common stone values and their kilogram equivalents:

Stone (st)	Kilograms (kg)
1	6.350
2	12.701
3	19.051
4	25.402
5	31.752
6	38.102
7	44.452
8	50.803
9	57.153
10	63.503
11	69.853
12	76.204
13	82.554
14	88.904
15	95.254
16	101.605
17	107.955
18	114.305
19	120.655
20	127.006

History & standards

The stone is an old English unit of mass equal to 14 avoirdupois pounds. It was used from at least the 14th century in England for weighing wool, livestock, and people. Because a stone is a whole multiple of the pound (14 lb), it meshes naturally with the pound and ounce system still familiar in the UK.

The stone was abolished as a legal unit of trade in the United Kingdom by the Weights and Measures Act 1985 — metric units became compulsory for commerce. Yet it persists strongly in everyday British and Irish conversation for body weight and is recognised by most healthcare providers in those countries. Its exact metric value is fixed by the 1959 International Yard and Pound Agreement: 1 stone = 14 × 0.45359237 kg = 6.35029318 kg.

The kilogram, the SI base unit of mass, was introduced during the French Revolution and since 2019 is defined by fixing the numerical value of the Planck constant, giving it a permanent, artefact-free definition.

Common applications

• Body weight in the UK and Ireland. GPs, practice nurses and patients routinely discuss weight in stone and pounds; metric electronic health records need converting for patient-facing communication.
• Weight-loss tracking. Many UK fitness apps and bathroom scales display weight in stone; gym members working with metric equipment need to convert.
• UK boxing weight classes. Weight categories (e.g. super-heavyweight >91 kg / >14 st 5 lb) are expressed in both units; coaches and athletes convert regularly.
• Ancestry and historical records. Pre-1985 UK census and health records state weight in stone; researchers need to convert to make comparisons with modern metric data.

Reverse conversion

To convert kilograms back to stone, divide by 6.35029: st = kg ÷ 6.35029 — or use our kg to stone calculator.

Limitations & gotchas

• Stone is not recognised in the US. Americans do not use stone; always give body weight in pounds or kg when communicating internationally.
• Stone and pounds vs decimal stone. 11.5 stone is not 11 stone 5 pounds. The decimal part must be multiplied by 14: 0.5 × 14 = 7 lb, so 11.5 st = 11 st 7 lb.
• Rounding. The exact factor is 6.35029318 kg/st; using 6.35 introduces an error of <0.005% — imperceptible for body-weight purposes.

Sources & references

• NIST SP 811 — Guide for the Use of the International System of Units (SI).
• BIPM — The International System of Units (SI), 9th edition (2019).
• 1959 International Yard and Pound Agreement (fixing 1 lb = 0.45359237 kg exactly; therefore 1 stone = 6.35029318 kg).
• UK Weights and Measures Act 1985 (abolishing stone as a legal unit of trade).