A firkin is an old English unit of volume. The name is derived from the Middle Dutch

Middle Dutch

Middle Dutch is a collective name for a number of closely related West Germanic dialects which were spoken and written between 1150 and 1500...

 word vierdekijn, which means fourth, i.e. a quarter of a full-size barrel.

Nor need you mind the serial ordeal

Of being watched from forty cellar holes

As if by eye pairs out of forty firkins.

— Robert Frost

Robert Frost

Robert Lee Frost was an American poet. He is highly regarded for his realistic depictions of rural life and his command of American colloquial speech. His work frequently employed settings from rural life in New England in the early twentieth century, using them to examine complex social and...

, "Directive"

For beer

Beer

Beer is the world's most widely consumed andprobably oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. It is produced by the brewing and fermentation of sugars, mainly derived from malted cereal grains, most commonly malted barley and malted wheat...

 and ale

Ale

Ale is a type of beer brewed from malted barley using a warm fermentation with a strain of brewers' yeast. The yeast will ferment the beer quickly, giving it a sweet, full bodied and fruity taste...

 a firkin is equal to nine imperial

Imperial unit

The system of imperial units or the imperial system is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced. The system came into official use across the British Empire...

 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, seventy-two 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 a quarter of a barrel

Barrel (unit)

A barrel is one of several units of volume, with dry barrels, fluid barrels , oil barrel, etc...

 (40.91481 litre

Litre

pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...

s). Casks in this size (themselves called firkins) are the most common container for cask ale

Cask ale

Cask ale or cask-conditioned beer is the term for unfiltered and unpasteurised beer which is conditioned and served from a cask without additional nitrogen or carbon dioxide pressure...

. A firkin is equal to half a kilderkin

Kilderkin

The kilderkin is an old English unit of volume equal to half a barrel or two firkins. It was used as standard size for brewery casks. The word kilderkin comes from Dutch for a small cask. The kilderkin has historically been in the general range of 16 to 18 gallons. Based on the current imperial...

.

For 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...

 the firkin had a larger size, namely a third of a tun

Tun (unit)

The tun is an old English unit of wine cask volume, holding about 954 litres, almost a cubic metre. Etymologically it is identical to the ton, a unit of mass or weight and constituted approximately 2,048 pints or pounds. Originally, it was a genuine unit of volume and measured 256 gallons ,...

. A tun being 210 gallons in the UK and 252 fluid gallons in the US, thus a wine firkin is about 318 l (318.226 or 317.975). It is also called tertian or, preferably, puncheon

Puncheon

Puncheon is a tool or instrument for piercing or punching, such as those used for impressing designs onto coin dies. The "barrel" meaning is thought to derive from the fact that it would have been marked by use of a punch to denote its contents....

 (in the US also shortened to pon).

Butter

Butter

Butter is a dairy product made by churning fresh or fermented cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications, such as baking, sauce making, and pan frying...

 and soap

Soap

In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...

 used to be sold by the firkin, too. In these cases it was a measure of weight, instead of volume: e.g., 56 lb

Pound (mass)

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

 (25.4 kg

Kilogram

The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

) and 64 lb (29.0 kg) respectively.

The term firkin is currently used to refer to antique wooden buckets, usually with wood handle and lid, about 10 inches (250 mm) high and 10 inches in diameter (about 10l or 2-3 dry gallons in capacity), formerly used to store sugar and other items.

The firkin (a firkin of water) is the base unit of mass in the humorous FFF System

FFF System

The Furlong/Firkin/Fortnight system is a set of units that uses impractical measurements not seriously deemed suitable for scientific or engineering use. The length unit of the system is the furlong, the mass unit is the mass of a firkin of water, and the time unit is the fortnight...

.