The tun (Old English: tunne, Latin: tunellus, Medieval Latin: tunna) is an English unit of liquid volume (not weight), used for measuring wine,[1] oil or honey.
The word tun is etymologically related to the word ton for the unit of mass, the mass of a tun of wine being approximately one long ton, which is 2240 pounds (1016 kg).
At some time before the 15th century, it was reduced to 252 wine gallons, so as to be evenly divisible by other small integers, including seven.
[nb 5] Standard tuns of wine came to serve as a measure of a ship's capacity.
[6] In the US customary system, the tun (symbol: US tu[7]) is defined as 252 US fluid gallons (about 954 litres).