- g (used only as part of the abbreviation mpg, for miles per gallon)
- Volume / capacity
- UK, Ireland, Canada, Guyana
The imperial gallon is a unit for measuring a volume of liquid or the capacity of a container for storing liquid, not the mass of a liquid. Thus, a gallon of one liquid may have a different mass from a gallon of a different liquid.
The U.S. liquid gallon and the U.S. dry gallon are different units defined by different means. The U.S. liquid gallon is defined as 231 cubic inches and equates to approximately 3.785 litres. One imperial gallon is equivalent to approximately 1.2 U.S. liquid gallons.
The U.S. dry gallon is a measurement historically applied to a volume of grain or other dry commodities. No longer commonly used, but most recently defined as 268.8025 cubic inches.
The imperial (UK) gallon is officially defined as 4.54609 litres.
The gallon is an ancient unit for measuring volume or capacity and has had numerous variations, both geographical and based on what substance was being measured.
In 1824 the imperial gallon was defined in the UK as being the volume of 10 lb of distilled water weighed using a particular method under specific atmospheric conditions. The Weights and Measures Act of 1963 refined the original description as the space occupied by 10 pounds (4.5 kg) of distilled water of density 0.998859 g/ml weighed in air of density 0.001217 g/ml against weights of density 8.136 g/ml.
Since the Weights and Measures Act of 1985, the imperial (UK) gallon has been officially defined as 4.54609 litres.
- A standard keg of draught beer in the UK contains 11 imperial gallons.
- An imperial gallon of petrol (gasoline) will power a typical UK 4-door family car (such as the Vauxhall Astra 1.4i) an average of 46.3 miles (74.5 Km).
- An imperial gallon of petrol (gasoline) will power a Porsche 911 (996) an average of 23.9 miles (38.5 Km).
In response to an EU directive, the imperial gallon was removed from the list of legally defined primary units of measure for trading and official purposes in Ireland in 1993 and the UK in 1994.
However, the gallon is still officially sanctioned for use as a secondary or supplementary unit, and is most commonly used publicly in reference to quantities of petrol (gasoline), and in trade for liquids for consumption such as beer, which is sold in barrels or kegs comprising standard multiples of an imperial gallon.
The imperial gallon is also often used in the UK to describe the capacity of containers storing large volumes of liquids, such as water butts.
In Canada, the imperial gallon is primarily used in reference to fuel economy. Gasoline is sold by the litre, but fuel economy is often expressed in the form of miles per gallon.
- Imperial gallons can be referred to as a multiple of several distinct units, but the unit most commonly referred to in the UK is pints.
- 1 imperial gallon = 8 pints
- 36 Imperial gallons = 1 Imperial (UK) Barrel