English brewery cask units

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. From the mid 15th century until 1803 in Britain "ale" casks and "beer" casks differed in the number of gallons they contained.