Tun The beer tun is equal to double the size of a butt: it is therefore exactly or approximately . This unit is exactly larger than the
wine tun.
Butt (imperial) The butt of beer is equal to half a tun or two hogsheads, and is therefore exactly or approximately .
Pin (imperial) A pin is equal to half a firkin, and is therefore exactly or approximately . This unit is exactly larger than a wine pin (one-eighth of a wine barrel or of a wine tun, i.e. 3.28125 imperial gallons or 3.9375 US gallons). Plastic versions of these casks are known as "polypins" and are popular in
homebrewing, the off-trade (deliveries for home consumption), and at beer festivals where non-standard beers are sold.
Gallon Originally, a 282 cubic inch ale or beer gallon was used. With the adoption of the
imperial system in the United Kingdom and its colonies, the system was redefined in terms of the
imperial gallon from 1824. ==Chart==