How this instrument works
A stone was once whatever lump of rock a market kept beside its balance, and its value depended on what you were buying: 14 lb for wool, 8 lb for butcher's meat, 12 lb for wax, 5 lb for glass. Britain's Weights and Measures Act of 1835 ended that local variation by fixing one stone at 14 pounds avoirdupois for every trade, and 14 lb is what a British bathroom scale still means by it.
That inheritance is why 6.35029318 is exact rather than rounded. On 1 July 1959, six national standards bodies signed an international yard and pound agreement that defined one avoirdupois pound as 0.45359237 kilogram — a definition, not a measurement. Multiply by fourteen and 6.35029318 kg falls out, a terminating decimal with no uncertainty hiding past its last digit. Since May 2019 that kilogram has itself rested on a fixed numerical value of the Planck constant, replacing Le Grand K, a platinum-iridium cylinder near Paris that had drifted roughly 50 micrograms away from its own sister copies.
Hardly anyone weighs cargo in stone now; Britain struck it from units permitted for trade in 1985. People are what survive. Ask a Briton or an Irish neighbour how heavy they are and you will hear eleven stone four, never 69.9 kilograms, while their GP's notes, drug doses and anaesthetic charts run wholly in kilograms. Horse racing handicaps are published in stone and pounds, British boxing reports fighting weights that way, and Australia and New Zealand dropped both during metrication. Americans never adopted stone at all: 154 pounds, flat.
- Type your weight into the Stone (st) field — it opens at 11 st, a middling adult figure.
- Holding a stone-and-pounds reading such as 11 st 4 lb? Divide those pounds by 14 first: 4 ÷ 14 = 0.2857, so type 11.2857.
- Read your answer on the Kilograms (kg) line, which recomputes on every keystroke.
- Working backwards from metric, divide kilograms by 6.35029318 — 70 kg returns 11.023 st, near enough eleven stone dead.
Worked example — eleven stone, converted for a chart
A bathroom scale in a hallway in Leeds reads 11 st. Type 11 into Stone (st) and the Kilograms (kg) line answers 69.85322498 kg. Every digit shown is genuine arithmetic: 11 × 6.35029318 approximates nothing, which is why its tail stops cleanly at an eighth decimal place instead of trailing off.
For a clinic form, round with judgement — 69.9 kg, or 70 kg where a whole number is wanted. A domestic scale is honest to perhaps ±0.2 kg, so those far decimals belong to arithmetic and not to any real measurement. Had that reading been 11 st 7 lb, half a stone above eleven, you would type 11.5 and get 73.02837157 kg.
Questions
Is 6.35029318 kg per stone exact, or has it been rounded?
Exact, with nothing chopped off. A pound equals 0.45359237 kilogram by definition under an international yard and pound agreement that took effect on 1 July 1959, and one stone is defined as fourteen of those pounds. Fourteen times 0.45359237 gives 6.35029318 and terminates there. Any rounding you meet came from a printed table or a phone app, never from this relationship itself.
How do I convert 11 st 4 lb into kilograms?
Handle each part separately, then add. Eleven stone is 11 × 6.35029318 = 69.85322498 kg, and 4 lb is 4 × 0.45359237 = 1.81436948 kg, so together they make 71.66759446 kg — call it 71.7 kg. Alternatively convert the whole reading to pounds first (11 × 14 + 4 = 158 lb) and multiply by 0.45359237. Both routes land on identical digits, because one is simply a rearrangement of the other.
Does 11.5 stone mean 11 stone 5 pounds?
No, and this trips up more people than any other part of the unit. A decimal fraction of a stone is a fraction of fourteen pounds, so 11.5 st is 11 st 7 lb, while 11 st 5 lb works out as 11.357 st. Multiply your leftover pounds by 1/14 before typing them: 5 ÷ 14 = 0.357. Reading 11.5 as eleven-and-five would cost you about 0.9 kg, roughly a bag of sugar.
Are British and American pounds the same weight?
Yes — imperial and US customary pounds have both equalled 0.45359237 kg since 1959, so no divergence creeps in through the pound itself. What differs is habit: stone never took hold in American speech, so a person there simply says 154 pounds rather than 11 stone. Their hundredweight also differs, being 100 lb rather than Britain's 112 lb, which is eight stone.
Can shops in Britain still sell goods by the stone?
Not for trade. The stone was dropped from units permitted in British commerce in 1985, and since 2000 goods sold by weight have been priced metrically, with pounds and ounces allowed only as supplementary indications. Nothing stops anyone stating their own body weight in stone, though, and the NHS accepts it conversationally while recording kilograms, since drug dosing is calculated per kilogram.
What is 70 kg in stone and pounds?
Divide by 6.35029318: 70 ÷ 6.35029318 = 11.0231 st. To recover pounds, multiply the fraction by 14, giving 0.0231 × 14 = 0.32 lb, so 70 kg is 11 st 0.3 lb — practically eleven stone dead. Note that the reverse factor, 1 ÷ 6.35029318 = 0.157473044…, never terminates, so metric-to-stone answers are always rounded somewhere even though the definition behind them is exact.