| Reference | Pints (pt) | Hectoliters (hL) |
|---|---|---|
| A teaspoon | 0.00879877 pt | 0.00005 hL |
| A can of soft drink | 0.580719 pt | 0.0033 hL |
| A wine bottle | 1.31982 pt | 0.0075 hL |
| A bathtub | 263.963 pt | 1.5 hL |
| An Olympic swimming pool | 4399385 pt | 25000 hL |
The pint in the imperial system is a unit of volume equal to exactly 568.26125 millilitres. Its symbol is pt. It is twenty imperial fluid ounces, an eighth of an imperial gallon, and half an imperial quart. It is the only imperial unit that most people in Britain and Ireland still use every week, and it survives because it is the legal measure for draught beer.
That legal status is precise. Draught beer and cider in the United Kingdom may be sold only in third-pints, half-pints and multiples of half a pint, and the glass itself must carry a verification mark certifying that it holds the stated measure. Publicans can be prosecuted for short measure, so the pint is one of the few units in daily life whose accuracy is actively policed.
Milk keeps the second foothold. Milk sold in returnable glass bottles may still be measured in pints, which is why doorstep deliveries are ordered by the pint while supermarket cartons carry litres. That split is a useful illustration of how metrication proceeded in Britain: it changed the shops and left the traditions alone.
The American pint is a different quantity and the difference is large. A United States liquid pint is 473 millilitres against the imperial 568, so a British pint is about a fifth bigger, and a traveller who orders a pint in New York receives noticeably less than one in Dublin. The American mnemonic that a pint's a pound the world around works only for the American pint; a British pint of water weighs a pound and a quarter.
That weight relationship was once the definition. The imperial system was built so that a gallon of water weighed ten pounds, which makes a pint weigh exactly a pound and a quarter, and the older British rhyme says so directly. Since 1985 the pint has been defined from the metric gallon instead, but the relationship still holds closely enough to be a useful check.
Below the pint the imperial chain runs to the gill at a quarter of a pint and the fluid ounce at a twentieth. Above it come the quart and the gallon. None of these steps is decimal, which is the reason the pint is now the only survivor: it is the one member of the chain that people handle directly, and the rest of the arithmetic has quietly moved to litres.
One imperial pint equals 568.26125 millilitres, 20 imperial fluid ounces, 0.125 imperial gallons, or about 1.201 US liquid pints.
The hectolitre is a unit of volume equal to one hundred litres, or a tenth of a cubic metre. Its symbol is hL. It is the trading unit of the drinks industry and of much of agriculture, and although almost nobody outside those trades ever writes it, within them it is the number that appears on every contract, licence and annual report.
Brewing runs on it entirely. A brewery's capacity is stated in hectolitres a year, duty is assessed on hectolitres produced, and the large international groups report annual volumes in hundreds of millions of them. A standard keg holds half a hectolitre, so the unit also happens to match the physical container the trade moves, which is part of why it stuck.
Wine regulation is written in the same terms. European appellation rules cap yield in hectolitres per hectare, a figure that does more than any other single number to define the character of an appellation, since a low cap concentrates the fruit and a high one dilutes it. Production statistics, stocks and the surpluses that periodically trouble the European market are all counted the same way.
Grain trading uses the unit in an unexpected direction. The hectolitre weight, or test weight, is the mass of grain that fills one hectolitre, and it is a standard quality specification: milling wheat is typically bought at 76 to 80 kilograms per hectolitre, and a load below the contracted figure is downgraded. The measurement works because well-filled, undamaged grain packs more densely than shrivelled grain does.
Dairy and other bulk liquids follow. Milk collection, fruit juice processing, edible oil and cider are all recorded in hectolitres, because the quantities involved are too large for litres to read comfortably and too small for cubic metres to be precise enough for duty and quality purposes.
For scale, a hectolitre is a large domestic water tank, a household bath filled about one and a half times, or a barrel of oil and a half. It converts to 22 imperial gallons or 26.4 United States gallons, and to 0.1 cubic metres exactly, which is the quickest route into SI-based calculations.
One hectolitre equals 100 litres, 0.1 cubic metres, about 26.4 US gallons, or about 22 imperial gallons.