The quart is a unit of volume (for either the imperial or United States customary units) equal to a quarter of a gallon (hence the name quart), two pints, or four cups. Since gallons of various sizes have historically been in use, quarts of various sizes have also existed; see gallon for further discussion. Three of these kinds of quarts remain in current use, all approximately equal to one litre. Its usual abbreviation is qt.
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United States liquid quart
All traditional U.S. length and volume measures have been legally standardized for commerce by the international yard and pound agreement of 1959 using the definition of 1 yard being exactly equal to 0.9144 meter. From this definition is derived the metric equivalencies for inches, feet, and miles; as well as area measures; and measures of volume. The US liquid quart equals 57.75 cubic inches, which is exactly equal to 0.946352946 litres.
United States dry quart
The US dry quart is equal to 1/4 of a US dry gallon, exactly 1.101220942715 litres.
Imperial quart
The imperial quart, used for both liquid or dry capacity, is equal to one quarter of an imperial gallon, or exactly 1.1365225 litres.
In French Canada, by federal law, the imperial quart is called pinte.
Winchester quart
The Winchester quart is an archaic measure, roughly equal to 2 Imperial quarts or 2.25 litres. The 2.5 litre bottles in which laboratory chemicals are supplied are sometimes referred to as Winchester quart bottles, although they contain slightly more than a traditional Winchester quart.
Reputed quart
The reputed quart was a measure equal to two thirds of an Imperial quart, or one sixth of a gallon, about 0.7577 litres. It was previously recognised as a standard size of wine bottle in the United Kingdom, and is only slightly larger than the current standard wine bottle of 0.75 litres.