Kilograms to Stones Converter

What this converter does

It converts kilograms to decimal stones — 80 kg becomes 12.6 st. The stone is a body-weight unit used in Britain and Ireland and effectively nowhere else, and the decimal form is what charts, spreadsheets and fitness apps use. If you want the conversational form of whole stones plus pounds, the dedicated stones-and-pounds converter linked below gives it directly, and most people ultimately want that one.

The formula

Divide kilograms by exactly 6.35029318. That constant is the stone in kilograms, and it is exact by definition rather than measurement: one stone is exactly 14 avoirdupois pounds, and the pound is exactly 0.45359237 kg, so 14 times 0.45359237 gives 6.35029318 with nothing rounded. The reverse multiplies by the same figure.

Worked examples

70 kg is 11.02 st. 80 kg is 12.60 st. 63.5029318 kg is exactly 10 st, which is worth noticing: the exact-stone values recur every 6.35029318 kg, so the whole ladder can be rebuilt from any one rung. 100 kg is 15.75 st. And a weight loss of 5 kg is 0.79 st — most of a stone, or about 11 lb, which is the translation most people actually want when a target is set in one system and measured in the other.

What a decimal stone means

It means tenths of a fourteen-pound unit, and it is not how anyone speaks. 11.5 st is eleven stone seven pounds, because half a stone is exactly 7 lb. 11.25 st is 11 st 3.5 lb. The decimal form exists because spreadsheets and charts need a single number, while conversation needs two. Both describe the same measurement; confusing them is the source of the most common error in this whole family, which is treating 11 st 4 lb as 11.4 st when it is actually 11.286 st.

Why the stone survives

The stone was once a genuine trade unit, with regional variants running from four to thirty-two pounds depending on the commodity — a stone of wool and a stone of beef were different amounts in the same market. The fourteen-pound stone was fixed for wool by statute in the fourteenth century and gradually became the stone; imperial standardisation in 1835 confirmed it. Metrication removed it from commerce, and it ceased to be lawful for trade in 1985, but it was never removed from speech. Body weight in Britain and Ireland is denominated in stones as a matter of culture, which is why no international form asks for it and why this conversion is needed so often.

Tracking a changing weight

Goals and measurements frequently arrive in different units, and holding the anchors makes the translation automatic. One stone is 6.35 kg. Half a stone is 3.18 kg. A steady loss of 0.5 kg a week is a little over a pound a week, so a stone takes about thirteen weeks at that rate. Running the arithmetic in kilograms and converting only for display keeps the trend honest, because the stones form quantises to the scale rounding and can show a flat week that was really a 0.4 kg change.

Precision and rounding

Both constants in the chain are exact definitions, so the conversion introduces no error and the display precision is entirely your choice. One or two decimal places suits body-weight tracking, since a tenth of a stone is 1.4 lb and a hundredth is 0.14 lb — already finer than domestic scales resolve. More decimals describe the arithmetic rather than the measurement.

Common mistakes

Reading a decimal stone as stones-and-pounds heads the list. Assuming Americans use stones is second — US body weight is pounds alone, so a US figure needs the pounds pages instead. Third is comparing against a printed chart and concluding the converter is wrong: charts round twice, first to whole pounds and often again to quarter stones, so they can legitimately sit a pound away from an exact figure without either being incorrect. The chart is coarser, not mistaken.

Benchmarks

50 kg is 7.87 st. 57.15 kg is exactly 9 st. 60 kg is 9.45 st. 63.5 kg is 10 st. 70 kg is 11.02 st. 76.2 kg is exactly 12 st. 80 kg is 12.60 st. 88.9 kg is exactly 14 st. 100 kg is 15.75 st. The exact-stone values at 57.15, 63.50, 69.85, 76.20, 82.55 and 88.90 kg are worth a glance, since they let you place any weight between two known rungs.

Accuracy and limits

Exact constants, exact arithmetic, display-only rounding. The converter accepts decimals and refuses ambiguous input with an explanation. It converts numbers faithfully and makes no medical judgement: what a given weight means for a given person is a question for a clinician, and body mass index, which this page is often reached in search of, is a separate and considerably cruder calculation.

Where stones appear outside the bathroom

Two British sports never metricated their weights. Horse racing sets jockey allocations in stones and pounds, and a rider who does eight stone seven is describing a professional qualification rather than a measurement. Boxing in the UK carries traditional weight-class names anchored in stones, sitting alongside the kilogram limits international bodies publish. Anyone reading a race card, an old fight record or a British sports archive needs exactly this conversion, which is part of why the unit has proved so durable.

Comparing against equipment ratings

Ladders, e-bikes, hammocks and gym equipment carry maximum user weights, and those ratings are published in kilograms almost everywhere. Converting your own weight to compare is the obvious use, and the one caution is direction: never round your weight down before checking it against a limit. A 150 kg rating is 23.6 st, and a rating exists to include a safety margin that pre-rounding quietly spends. Convert exactly, then compare.

Half stones, quarter stones and scale graduations

Older UK bathroom scales are graduated in stones with quarter or half-stone marks, which map cleanly onto decimals: a quarter stone is 0.25 st or 3.5 lb, and a half is 0.5 st or 7 lb. A scale reading between marks resolves no better than about 1.6 kg, which is worth remembering before recording a converted figure to two decimal places. The converter is exact; the dial that produced the input was not, and the honest record reflects the coarser of the two.