Article — Stone Weight Converter (UK)
Stone weight converter: stones, pounds, and kilograms
One stone equals exactly 14 pounds or 6.35029 kilograms. UK convention writes body weight as "X st Y lb" — for example, 11 st 7 lb equals 73 kg. The unit remains common in the UK, Ireland, and parts of the Commonwealth despite official metric adoption.
The stone is one of those measurement units that refuses to disappear. Britain went metric for trade in 1965 and for currency in 1971, but body weight in stones survived. If you ask a typical British adult what they weigh, they will give an answer in stones and pounds before they think about kilograms. This converter handles all three units with the exact factors.
What is a stone in weight?
A stone is a unit of mass equal to exactly 14 avoirdupois pounds. Through the international pound definition (1 lb = 0.45359237 kg), one stone equals exactly 6.35029318 kg. The unit is part of the British Imperial system and remains in everyday use for body weight measurement in the United Kingdom, Ireland, and several Commonwealth countries.
The word "stone" comes from the medieval practice of using physical stones as standard weights. Markets across England kept calibrated stones for weighing goods. Different goods used different stone values — wool was weighed in 14-pound stones, meat in 8-pound stones, glass in 5-pound stones. The 14-pound stone for body weight became universal under the 1835 Weights and Measures Act.
Stone to kilogram conversion
The exact conversion is 1 stone = 6.35029 kg. To convert stones to kilograms, multiply by 6.35029. To convert kilograms to stones, divide by 6.35029. For mental math, 1 stone ≈ 6.4 kg works within 1% accuracy: 10 stones × 6.4 = 64 kg (true: 63.5 kg).
When converting back from kilograms to stones + pounds, the procedure is: divide kg by 6.35029 to get decimal stones. Take the integer part as whole stones. Multiply the decimal remainder by 14 to get extra pounds. For 73 kg: 73 / 6.35 = 11.49 stones → 11 stones; 0.49 × 14 = 6.9 lb → 11 st 7 lb.
The stone has historically been used for personal body weight in the UK and Ireland; it was phased out of formal trade with metrication. Trading goods like potatoes or coal in stones was technically against the Weights and Measures Act until the change. Body weight measurement was never regulated because it is not a commercial transaction.
The stone + pounds format
British convention writes body weight as a stones component plus a pounds remainder. The pounds value is always between 0 and 13 — 14 pounds would round up to one more stone. So 11 st 14 lb is incorrect; it should be 12 st 0 lb. Some traditional sources write it more compactly as "12 stone" with no zero pounds.
Spoken form: "eleven stone seven" means 11 st 7 lb. Some speakers drop the "pounds" but never the "stone." A US speaker might say "73 kilograms" or "161 pounds"; a UK speaker would say "eleven stone seven." The two systems exist side by side in NHS clinics, where weight is recorded in kilograms but explained to patients in stones.
Where stones are still used
Stones remain in daily use for personal body weight in the UK, Ireland, Australia, and New Zealand. Older generations use it almost exclusively; younger generations increasingly think in kilograms. The NHS uses kilograms in clinical records but stones in patient-facing discussions, because that is what most patients know.
The unit also appears in sports — UK boxing and weightlifting historically used pounds and stones, though modern international competition uses kilograms. Horse racing in the UK uses stones for jockey weight (a typical flat-race jockey weighs 7-9 stones). Rugby and football teams sometimes quote player weights in stones, especially in older media.
Outside these countries, stones are essentially unused. The United States never adopted them — Americans use pounds. Continental Europe uses kilograms exclusively. Most of Asia and Africa use kilograms. Canada uses both pounds and kilograms for body weight, with kilograms dominant in medical contexts.
A short ton (US ton) is 2,000 pounds = 142.86 stones, while a long ton (British ton, rare today) is 2,240 pounds = 160 stones. Some old UK documents quote 160 stones as "1 ton" but this means the British long ton, not the US short ton. Modern UK use almost always means metric tonnes (1,000 kg = 157.5 stones).
Typical body weight in stones
UK adult averages from the 2021 ONS Health Survey: women about 10 st 7 lb (66.7 kg), men about 12 st 8 lb (79.8 kg). The UK averages have risen 1.5 stones (about 9.5 kg) since the 1990s, mostly in the 25-44 age band. Public health discussion regularly uses both stones and BMI to discuss weight gain trends.
Body weight categories in stones: under 7 stones is very low for an adult; 7-10 stones covers most slim and average adults; 10-13 stones is a broad middle range; 14+ stones is heavier than average. BMI thresholds at 5'7" (170 cm) average UK height: BMI 25 ≈ 11 st 5 lb; BMI 30 ≈ 13 st 5 lb. The calculator displays decimal stones alongside the conventional st+lb format.
Historical stone units
Before the 1835 standardization, different goods used different stone weights. Wool: 14 lb. Cheese: 16 lb. Glass: 5 lb. Meat in London: 8 lb. Meat in Hertfordshire: 12 lb. The variation reflected the practical handling weight for each commodity — wool sacks held conveniently as 14-pound bundles, while glass sheets were managed in 5-pound stacks.
The 1835 act fixed the body-weight stone at 14 pounds, which had been the most common usage for centuries. Other stone values gradually disappeared from commerce. The historical variation occasionally surfaces in old measurements found in ancient documents, where a "stone" might mean anything from 5 to 24 pounds depending on the trade and region.
When reading historical UK weight records, always check the unit context. A pre-1835 document quoting "120 stone of wool" used the 14-pound wool stone (so 1,680 lb = 762 kg). The same document quoting "120 stone of meat" might use the 8-pound meat stone (so 960 lb = 435 kg). Modern stone is unambiguous at 14 pounds.
Common stone weight mistakes
Mistake one is writing decimal stones in British format. "11.5 stones" is mathematically correct but reads as awkward to British speakers, who would say "11 stone 7 pounds." Decimal stones appear in scientific and clinical contexts but not in everyday speech. Mixed st+lb is the convention.
Mistake two is rounding the pounds remainder past 14. Writing 11 st 14 lb instead of 12 st 0 lb is technically incorrect — the pounds remainder always stays between 0 and 13. The calculator handles this automatically: any input of 11 st 14 lb is treated as 12 st 0 lb internally.
Mistake three is forgetting that the UK pound is the avoirdupois pound (16 ounces). The Apothecaries' pound (12 ounces) and Troy pound (12 ounces) still exist for medicines and precious metals, but they are not used for body weight. When someone says "11 stone 7 pounds," they always mean 11 × 14 + 7 = 161 avoirdupois pounds.
1 stone 14 lb (exact)1 stone 6.35029 kg (exact)kg from st st × 6.35st from kg kg ÷ 6.35UK woman avg 10 st 7 lb (66.7 kg)UK man avg 12 st 8 lb (79.8 kg)- 14 pounds = 1 stone (exact, since 1835)
- 6.35029 kg = 1 stone (exact, from 1959 international pound)
- 6.4 kg mental approximation, 1% off
- 0 to 13 lb valid pounds remainder in UK convention
- 1835 Weights and Measures Act fixed stone at 14 lb
- 1985 UK formally legalized stone for retail trade
- UK average woman 10 st 7 lb (66.7 kg)
- UK average man 12 st 8 lb (79.8 kg)