| Reference | Quarts (qt) | Centiliters (cL) |
|---|---|---|
| A teaspoon | 0.00439938 qt | 0.5 cL |
| A can of soft drink | 0.290359 qt | 33 cL |
| A wine bottle | 0.659908 qt | 75 cL |
| A bathtub | 131.982 qt | 15000 cL |
| An Olympic swimming pool | 2199692 qt | 250000000 cL |
The quart in the imperial system is a unit of volume equal to exactly 1136.5225 millilitres. Its symbol is qt. It is two imperial pints and a quarter of an imperial gallon, and its name says so: quart comes from the Latin quartus, a fourth. It sits between the pint and the gallon and, in Britain, it has lost to both.
Its decline is the clearest case of a unit being squeezed out from both sides. The pint survived because it is the legal measure for draught beer and because a person can hold one; the gallon survived in fuel economy figures. The quart is neither drunk nor driven, so nothing kept it in daily speech, and British shops now describe the same quantity as a litre or as two pints.
In the United States the same name is thriving. A United States liquid quart is 946 millilitres, and milk, cream, stock, ice cream, paint and motor oil are all sold in that size. An engine oil change is quoted in quarts, five being typical for a car, and the quart carton is one of the most recognisable objects in an American kitchen.
That American survival owes something to the litre. A United States quart is only five per cent smaller than a litre, so shelf sizes barely changed when Canadian and international products moved to metric, and a shopper comparing a quart with a litre is comparing almost the same thing. The imperial quart is thirteen per cent larger than a litre, which made the same substitution less comfortable in Britain.
The dry measure adds a further complication in the United States. A dry quart is 1101 millilitres against the liquid quart's 946, and it belongs to a separate chain used for berries, produce and grain. Nothing on a label distinguishes them, so the same word describes two different quantities depending on whether the contents pour or not.
For conversion, the imperial quart is 1.1365 litres and the United States liquid quart is 0.9464. The rule of thumb that a quart is roughly a litre is safe in America and about a seventh out in Britain, which is exactly the kind of margin that turns a recipe or a chemical dilution wrong without looking obviously wrong.
One imperial quart equals 1136.5225 millilitres, 2 imperial pints, 0.25 imperial gallons, or about 1.201 US liquid quarts.
The centilitre is a unit of volume equal to one hundredth of a litre, or ten millilitres. Its symbol is cL, and the lower-case cl is also used. Unlike most centi-prefixed units it has a real commercial life, because it happens to be the size that suits drink labelling, and in several countries it is the form printed on almost every bottle.
Drink containers are its main employment. In France, Belgium, Italy and Spain a wine bottle is labelled 75 cL, a beer 33 or 50 cL, a soft drink 33 cL, and a spirits miniature 5 cL. The same containers carry 750 ml and 330 ml in Britain, Germany and most of the English-speaking world, which is why identical bottles appear to bear different numbers depending on where they were filled.
Bar measures follow the same split. A standard spirit serving is 4 cL in France and 2 or 4 cL in Germany and Austria, while Britain pours 25 or 35 millilitres and the United States uses fluid ounces. European cocktail recipes are written in centilitres throughout, so a classic proportion of six parts to three to one appears as 6 cL, 3 cL and 1 cL, which reads more cleanly than the millilitre equivalents.
There is no legal difference between the forms. European Union labelling rules accept millilitres, centilitres and litres, so the choice is a matter of national typographic habit rather than of regulation. Where centilitres are used, the number on a bottle stays between one and a hundred for every ordinary container size, which is exactly the range a prefix is supposed to deliver.
The unit is also easy to picture. Ten millilitres is two teaspoons, a generous mouthful of water, or the dose measure supplied with a bottle of cough syrup. A tablespoon is one and a half centilitres, an espresso is about three, and a wine glass poured to a standard measure is twelve to fifteen.
Converting between systems needs some care because a centilitre falls between the two customary small measures. It is 0.338 United States fluid ounces and 0.352 imperial fluid ounces, so neither reads as a round number, and drink volumes converted between Europe and North America almost always end up rounded rather than exact.
One centilitre equals 10 millilitres, 0.01 litres, about 0.338 US fluid ounces, or about 0.352 imperial fluid ounces.