Tun (unit)
Encyclopedia
The tun is an old English unit
English unit
English units are the historical units of measurement used in England up to 1824, which evolved as a combination of the Anglo-Saxon and Roman systems of units...

 of wine
Wine
Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...

 cask volume, holding about 954 litres
1 E-1 m³
To help compare different orders of magnitudes this page lists volumes from at 10-1 m³ to 1 m³. See also volumes or capacities of other orders of magnitude.*Volumes smaller than 100 litres*0.1 m³ is equal to:...

, almost a cubic metre
Cubic metre
The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...

. Etymologically it is identical to the ton
Ton
The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of weight, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term.It is derived from...

, a unit of mass or weight and constituted approximately 2,048 pint
Pint
The pint is a unit of volume or capacity that was once used across much of Europe with values varying from state to state from less than half a litre to over one litre. Within continental Europe, the pint was replaced with the metric system during the nineteenth century...

s or pound
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...

s. Originally, it was a genuine unit of volume and measured 256 gallon
Gallon
The gallon is a measure of volume. Historically it has had many different definitions, but there are three definitions in current use: the imperial gallon which is used in the United Kingdom and semi-officially within Canada, the United States liquid gallon and the lesser used United States dry...

s (28), which is the base for the name of the quarter of 64 corn gallons. The approximate weight of water (or wine) per gallon is 8 pounds, and 8 x 256 gallons = 2,048 pounds; hence a tun 'is' a ton. Its later division into 210 imperial or 252 wine gallons was chosen to be evenly divisible by small integers, including seven:
210 = 2×3×5×7
252 = 2²×3²×7

Queen Anne’s
Anne of Great Britain
Anne ascended the thrones of England, Scotland and Ireland on 8 March 1702. On 1 May 1707, under the Act of Union, two of her realms, England and Scotland, were united as a single sovereign state, the Kingdom of Great Britain.Anne's Catholic father, James II and VII, was deposed during the...

 wine gallon
Wine gallon
A wine gallon is a unit of capacity that was used routinely in England as far back as the 14th century, and by statute under Queen Anne since 1707. Britain abandoned the wine gallon in 1826 when it adopted imperial units for measurement...

 is 231 cubic inch
Cubic inch
The cubic inch is a unit of measurement for volume in the Imperial units and United States customary units systems. It is the volume of a cube with each of its 3 sides being one inch long....

es (3×7×11 in³), which makes the tun based on it exactly 2²×3³×7²×11 = 58,212 in³, which is a cylinder with diameter and height of 42 in both (if you approximate  by 22/7).

Beer

It is assumed that the tun once also was the base for English brewery casks, whose now largest measure, the hogshead
Hogshead
A hogshead is a large cask of liquid . More specifically, it refers to a specified volume, measured in either Imperial units or U.S. customary units, primarily applied to alcoholic beverages such as wine, ale, or cider....

, is of a similar magnitude as its wine equivalent (between 220 and 250 litres). A different gallon was used for ale and beer, the ale gallon, which in modern times was 282 cubic inches (2×3×47 in³), which does not divide the 58,212 in³ conveniently.
There also were other, sometimes foreign tuns/tons, for example at least until the 16th century one of 240 gallons, grouped in 60 sesters of 4 gallons each.
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