Capacities of brewery casks were formerly measured and standardised according to a specific system of English units. The system was originally based on the ale gallon of 282 cubic inches (4.62 L; 1.22 US gal). In United Kingdom and its colonies, with the adoption of the imperial system in 1824, the units were redefined in terms of the slightly smaller imperial gallon (1.2 US gal; 4.5 L). The older units continued in use in the United States.
Historically the terms beer and ale referred to distinct brews.[nb 1] From the mid 15th century until 1803 in Britain "ale" casks and "beer" casks differed in the number of gallons they contained.
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