Article — Stone to Kg Converter
Stone to kg conversion explained
One stone equals exactly 6.35029318 kilograms. The factor comes from the avoirdupois pound, fixed at exactly 0.45359237 kg by the 1959 International Yard and Pound Agreement, multiplied by 14. To convert stone to kg, multiply by 6.35029. To go from kg to stone, divide by the same number.
The stone remains a working unit in the United Kingdom and Ireland for adult body weight, even though both countries adopted metric measures for trade decades ago. The conversion is short, exact, and useful for clinical paperwork, fitness tracking, and travel.
What stone to kg means
The stone is a unit of mass equal to 14 pounds. It survived the British metrication push of the 1970s for one reason: people kept weighing themselves in it. Modern UK bathroom scales display both stone and kilograms, and clinicians often ask patients for stone first, then write kilograms in the chart.
One stone weighs 6.35029318 kg. That number is not a rounded measurement. The avoirdupois pound has been fixed at exactly 0.45359237 kg since the 1959 International Yard and Pound Agreement, and the stone has been fixed at 14 pounds since the UK Weights and Measures Act 1835. Multiply and you get a defined value, not an approximation.
The stone was banned from use in trade by the UK Weights and Measures Act 1985, but it remains legal for personal and informal use. That is why bathroom scales still ship with a stone dial in Britain.
The stone to kg formula
The conversion is one multiplication. Kilograms equal stone times 6.35029318. For everyday work, 6.35 is close enough.
1 st 6.35029 kg10 st 63.50 kg14 st 88.90 kgkg = st × 6.35 st = kg / 6.35The reverse direction divides. To turn 70 kg into stone, compute 70 / 6.35029 = 11.0231 stone. Multiply the decimal remainder (0.0231) by 14 to get the leftover pounds, 0.32 lb. So 70 kg reads as 11 st 0.3 lb on a UK scale.
Why the stone survived in the UK
Medieval merchants used real stones as counterweights on balance scales. Different trades used different stones for different goods, and a butcher’s stone might weigh differently from a wool stone. The Statute of Weights of 1303 began the standardisation, and by the sixteenth century the wool stone of 14 pounds had taken over for most commodities.
Britain shifted to metric for commerce in stages between 1965 and 1995. Trade paperwork now uses kilograms. Personal weight slipped through that net. The stone carried a sense of mental scale that grams and kilograms did not match for a nation raised on imperial units, and the habit stuck across generations.
Stone to kg in NHS and medical use
NHS clinical records are metric. Charts, prescriptions, and research use kilograms. The intake conversation, though, often starts in stone. A patient says “12 stone 7,” the nurse converts mentally to 79.4 kg, and that goes in the record.
If a UK clinician asks for your weight, give both numbers. Stone helps them gauge your build at a glance; kilograms feed the BMI calculation and any medication dosing.
For BMI, kilograms are required. The formula divides weight in kilograms by height in metres squared. Imperial BMI exists but uses inches and pounds with a 703 multiplier, and rounding tends to drift.
Stone to kg reference table
- 8 st = 50.80 kg, lower end of healthy adult weight
- 10 st = 63.50 kg, average for shorter UK adults
- 12 st = 76.20 kg, near the UK male mean
- 14 st = 88.90 kg, overweight for most heights
- 15 st = 95.25 kg, BMI 31 at 1.75 m height
- 18 st = 114.31 kg, severely obese for most heights
- 20 st = 127.01 kg, near the UK bariatric clinic threshold
Stone and pounds to kg together
UK weights often come as stone plus pounds. To convert, multiply the stone part by 6.35029, multiply the pounds part by 0.45359, and add. The result is the kilogram value.
Take 12 stone 7 pounds. The stone part gives 76.2036 kg. The pounds part gives 3.1751 kg. The total is 79.38 kg. The same answer comes from a single shortcut: convert everything to pounds first (12 × 14 + 7 = 175 lb), then multiply by 0.45359. Both methods agree.
A common error is to convert the stone part and then add the leftover pounds as if they were kilograms. Pounds are not kilograms. Always multiply the pounds by 0.45359 first, then add.
Common stone to kg mistakes
The first trap is treating the stone like a 6 kg unit. Six is close, but the real factor is 6.35029, and rounding shifts a 15 stone weight by nearly 5 kg if you use 6 instead. The second trap is mixing pound and kilogram in the same step, described above. The third trap is using a different definition of stone.
Older trade documents in Britain and Ireland refer to wool stones (14 lb), butcher stones (8 lb), and even a Cornish “heavy stone” of 16 lb. For modern body weight, the only definition that applies is the avoirdupois stone of 14 pounds. If a recipe or historical text uses stone for produce, check the period; commercial stones varied.
Stone to kg for BMI and fitness
Most BMI calculators and fitness apps want kilograms and metres. Stone to kg conversion is the first step. After that, BMI is weight divided by height squared in metres, no extra factors. A weight of 12 st 7 lb (79.38 kg) at 1.75 m gives a BMI of 25.9, on the edge of the overweight range as defined by the WHO.
UK fitness culture often tracks loss in stone. “Down two stone” reads as a clean milestone, while “down 12.7 kg” feels abstract. The numbers describe the same loss; the framing differs. Personal trainers in Britain still take goals in stone and convert internally; commercial weight-loss programmes such as those run through GP referrals report progress both ways.
The stone is unusual among historical units because it sits inside a fully metric legal system without contradiction. Trade is metric. Personal weight is stone. Both numbers are exact, both are accepted, and the converter above moves between them without rounding the underlying factor. For a fitness log, two decimals are plenty. For a clinical record, the same conversion holds regardless of precision.