| Reference | Stones (st) | Hundredweights (cwt) |
|---|---|---|
| A sheet of A4 paper (80 gsm) | 0.000787365 st | 0.0000984207 cwt |
| One litre of water | 0.157473 st | 0.0196841 cwt |
| Average adult human | 11.0231 st | 1.37789 cwt |
| A small car | 220.462 st | 27.5578 cwt |
The stone is a unit of mass equal to 14 pounds, or about 6.35029 kilograms. Its symbol is st. It is a British unit with an unusual property: it is almost entirely confined to one purpose, human body weight, and almost entirely confined to Britain and Ireland.
Before standardisation the stone was not a fixed quantity at all. It varied by commodity and by region, from eight pounds for meat to twenty-four for certain wools, and a stone of one good was simply not a stone of another. The Weights and Measures Act of 1835 fixed it at fourteen pounds for all purposes, ending a genuine source of commercial dispute.
Its survival is a study in how measurement habits actually change. Britain converted trade to metric units over decades, and shops now weigh in kilograms, but personal weight remained stubbornly in stones and pounds. A person who buys potatoes by the kilogram will still say they weigh eleven stone four. Medical practice sits awkwardly between the two, with charts in kilograms and patients who think in stones, so most clinical software displays both.
The convention is to give a whole number of stones followed by the remaining pounds, never a decimal, so twelve stone six means 174 pounds. This makes mental conversion to metric awkward and is one reason the unit has no traction outside its home. Ireland uses it similarly, and Australia and New Zealand abandoned it in the 1970s.
Sport keeps the unit visible where medicine has quietly dropped it. British boxing reports fighters at, say, twelve stone seven, horse racing states the weight a jockey must carry in stones and pounds, and rowing crews are selected against a stone-based limit. Clinical practice has moved the other way: hospital notes, drug dosing and growth charts are all metric, because a dose calculated per kilogram cannot safely pass through a conversion. The result is that many British patients hear their weight in kilograms from a nurse and repeat it in stones to a friend an hour later, translating in their heads at roughly six and a third kilograms to the stone.
One stone equals 14 pounds, about 6.35029 kilograms, or 224 ounces.
The hundredweight is a unit of mass whose value depends on which side of the Atlantic you are standing. The imperial or long hundredweight is 112 pounds, about 50.802 kilograms. The US or short hundredweight is 100 pounds, about 45.359 kilograms. Its symbol is cwt, from the Latin centum and the English weight.
The name promises a hundred and the imperial version delivers a hundred and twelve, which looks like an error until the arithmetic behind it is seen. Twenty hundredweight make a long ton of 2240 pounds, and a hundredweight is eight stone of fourteen pounds each. The chain of halvings and doublings that runs from the pound to the ton only closes neatly if the intermediate unit is 112, so the number is a consequence of the system rather than a mistake in it.
Its working life was in bulk trade. Coal, cement, grain, potatoes and fertiliser moved by the hundredweight, and sack sizes were built around it: the standard British coal sack held one hundredweight, which is why a coal merchant's cart was rated in a number of hundredweight rather than in tons. Vans and light trucks were once classified the same way, and the phrase survives in some vehicle names.
In the United States the short hundredweight is still used in agricultural markets, where livestock, grain and milk prices are quoted per hundredweight rather than per pound or per ton. Elsewhere the unit has largely given way to the tonne and the kilogram, and its main modern role is to make old records intelligible.
Continental Europe kept a cousin of it under a different name. The quintal, from the Arabic qintar by way of medieval Latin, served the same purpose in French, Spanish, Italian and Portuguese trade, and when the metric system arrived it was simply redefined as a round 100 kilograms. That metric quintal is still the unit in which grain harvests are reported across much of southern Europe, Latin America and India, and it sits close enough to the imperial hundredweight of 50.8 kilograms that old and new figures can look deceptively similar. The parallel is instructive: both units survived because a sack a strong worker could handle is a more natural quantity than any round metric mass.
One imperial hundredweight equals 112 pounds, about 50.802 kilograms, or 8 stone.