What is a Stone (st)?
Formal Definition
The stone (symbol: st) is a unit of mass in the British imperial system equal to 14 avoirdupois pounds or approximately 6.35029 kilograms. It is used primarily in the United Kingdom and Ireland for expressing human body weight. One stone equals 14 pounds, 224 ounces, or 6.35029 kg.
Body Weight Unit
The stone's primary modern use is for discussing human body weight in the UK and Ireland. A British person might describe their weight as "11 stone 4" (meaning 11 stone and 4 pounds, or 158 pounds / 71.7 kg). This convention is deeply ingrained in British and Irish culture, even as metric units have replaced imperial measures for most other purposes.
Relationship to Other Units
The stone relates to other imperial weight units: 1 stone = 14 pounds = 224 ounces. Two stones equal one quarter (28 lbs), and eight stones equal one hundredweight (112 lbs in the British system). These relationships reflect the medieval English system of weights used for trade.
Etymology
Literal Origin
The word "stone" as a unit of weight derives from the ancient practice of using actual stones as counterweights on balance scales. This practice is documented in virtually every ancient civilization. The Book of Deuteronomy warns against having "diverse weights, a great and a small" — referring to the stone weights used in trade.
Variable Stones
Historically, the stone varied enormously depending on the commodity being weighed and the locality. A stone of wool was 14 pounds, but a stone of glass was 5 pounds, and a stone of lead was 12 pounds. Different cities had different stone weights. The 14-pound stone eventually became the legal standard in England, but the variability persisted in some trades into the 19th century.
Legal Standardization
The Weights and Measures Act of 1835 defined the stone as exactly 14 avoirdupois pounds for all purposes, eliminating the commodity-specific variations. This definition has remained unchanged since then.
Precise Definition
Definition
The stone is defined as exactly 14 avoirdupois pounds. Since one avoirdupois pound is defined as exactly 0.45359237 kilograms (by the 1959 international agreement), one stone equals exactly 6.35029318 kilograms.
Legal Status
The stone was included in the UK Weights and Measures Act of 1985 as a unit for personal body weight. Under EU regulations, the stone was not recognized as a primary unit of trade, but its use for body weight has been specifically exempted. The UK continues to recognize the stone for this purpose after Brexit.
Not Used in the US
The stone was never officially adopted in the United States. Americans express body weight in pounds only ("I weigh 170 pounds"), while Britons use stones and pounds ("I weigh 12 stone 2"). This is one of the notable differences between American and British English measurement conventions.
History
Ancient Roots
Using stones as weights is one of the oldest measurement practices, dating back to at least 3000 BC. Ancient Mesopotamian and Egyptian merchants used polished stone weights on balance scales. The specific practice of calling a fixed weight "a stone" developed in medieval England.
Medieval Commerce
In medieval England, the stone was used extensively in trade, but its weight varied by commodity. The most important variation was for wool — England's chief export. The stone of wool was standardized at 14 pounds in 1389 by a statute of Richard II. Other commodities retained different stone weights: a stone of butcher's meat was 8 pounds, and a stone of cheese could be 16 pounds.
19th Century Standardization
The Weights and Measures Act of 1835 unified the stone at 14 pounds for all purposes, ending centuries of confusion. The same act established the hundredweight at 112 pounds (8 stone) and the ton at 2240 pounds (160 stone). These multiples were specific to the British system — the American hundredweight is 100 pounds and the American ton is 2000 pounds.
Metrication and Survival
When the UK began metrication in the 1960s, the stone was expected to disappear. However, it proved remarkably resilient for body weight measurement. Despite official metrication, British people continued to discuss their weight in stones and pounds. Medical records in the UK now use kilograms, but patients typically report their weight in stones. This dual system persists today.
Cultural Significance
The stone has become a cultural marker distinguishing British English from American English. Americans find the stone confusing, and Britons find the American practice of stating large pound numbers equally unintuitive. "I weigh 165 pounds" sounds awkward to a Briton, just as "I weigh 11 stone 11" sounds strange to an American.
Current Use
Body Weight in the UK
The stone is used daily by millions of people in the UK for discussing body weight. Bathroom scales sold in the UK display weight in stones and pounds (or offer stones as an option alongside kilograms). Weight loss programs, fitness magazines, and health articles aimed at British audiences use stones. The NHS uses kilograms in medical records but stone/pound conversions are commonly provided.
Body Weight in Ireland
Ireland follows the same convention as the UK, using stones and pounds for body weight in everyday conversation. Irish medical practice uses kilograms officially, but patients commonly describe their weight in stones.
Sports
In boxing, horse racing, and some other sports in the UK and Ireland, weight classes and descriptions use stones and pounds. A jockey might need to "ride at 8 stone 7" (119 lbs / 54 kg). Boxing weight descriptions in British media use stones.
Declining Use
The stone is gradually declining in use, particularly among younger Britons who are more comfortable with kilograms. However, it remains deeply embedded in British culture and shows no signs of disappearing in the near future. Many British adults know their weight in stones but would struggle to state it in kilograms without converting.
Everyday Use
The Weight Conversation
In British and Irish daily life, the stone is primarily encountered in conversations about body weight. "I've lost half a stone" (7 lbs / 3.2 kg) or "I need to lose a stone" (14 lbs / 6.35 kg) are common statements. Weight loss milestones are often marked in stones.
Bathroom Scales
Bathroom scales sold in the UK typically offer three modes: kilograms, stones/pounds, and pounds only. The stones/pounds mode remains the most popular choice among British adults. Digital scales display readings like "10 st 7 lb."
Health and Fitness
British weight loss programs (like Slimming World and Weight Watchers UK) track progress in stones and pounds. Fitness magazines and websites aimed at UK audiences report weight in stones. BMI calculators for British users accept input in stones and pounds.
Horse Racing
In British and Irish horse racing, the weight a horse carries (jockey plus saddle and equipment) is expressed in stones and pounds. Handicap weights might be "9 stone 2" or "10 stone 7." Jockeys are described by their riding weight in stones.
In Science & Industry
No Scientific Use
The stone has no role in scientific measurement. All scientific work uses SI units (kilograms and grams). The stone is purely a cultural unit used for expressing human body weight in British and Irish daily life.
Medical Context
British medical practice officially uses kilograms for patient weight. However, clinicians routinely convert between stones and kilograms when communicating with patients. Drug dosages are always calculated in kilograms, never stones. Medical research publications use kilograms exclusively.
Historical Records
Historical documents in English-speaking countries may express weights in stones, requiring conversion for modern scientific use. Converting stones to kilograms is straightforward: multiply by 6.35029.
Interesting Facts
A stone (14 lbs) is roughly the weight of a typical house cat or a bowling ball. Losing "a stone" — a common British weight-loss goal — means losing about 6.35 kg.
In medieval England, the stone of wool (14 lbs) was different from the stone of glass (5 lbs), the stone of wax (12 lbs), and the stone of lead (12 lbs). The 14-pound stone won out only because wool was England's most important export commodity.
Americans and Britons often struggle to understand each other's body weight statements. "I weigh 154 pounds" and "I weigh 11 stone" mean the same thing, but neither sounds natural to the other's ears.
The British hundredweight (112 lbs = 8 stone) differs from the American hundredweight (100 lbs). Similarly, the British long ton (2240 lbs = 160 stone) differs from the American short ton (2000 lbs). These differences trace back to the stone.
Jockeys in British and Irish horse racing must meet strict weight requirements measured in stones. Some jockeys maintain body weights as low as 7 stone 12 (110 lbs / 50 kg) through rigorous diet and exercise.
The stone was never widely used in continental Europe, making it a distinctly British and Irish unit. Even other former British colonies like Australia, Canada, and South Africa abandoned the stone during metrication.
Despite decades of official metrication, a 2019 survey found that the majority of British adults still prefer to state their body weight in stones rather than kilograms.
Regional Variations
United Kingdom
The stone is in active daily use for body weight throughout the UK. It is understood by all adults and used across all social classes. British bathroom scales, health magazines, and weight management programs all support stones.
Ireland
Ireland follows the same convention as the UK, using stones for body weight despite official metrication. The stone is as culturally embedded in Ireland as in Britain.
Former British Colonies
Australia, New Zealand, Canada, and South Africa all used the stone historically but abandoned it during metrication (1970s-1980s). Older residents of these countries may still remember their weight in stones, but younger generations use kilograms exclusively.
The United States
The stone was never commonly used in the US. Americans use pounds for body weight ("I weigh 180 pounds") and have no familiarity with the stone. American medical and fitness contexts use pounds exclusively.