Imperial Gallon (gal (UK))

Imperial (British)Current unit

Exactly 4.54609 liters, the volume of 10 pounds of water. Used for fuel economy in the UK (miles per gallon) and historically across the Commonwealth.

1 imperial gallon = 4.54609 liters (exactly).

About the imperial gallon

Britain unified its confusing gallons by act of Parliament in 1824. Before then, the country used separate ones for wine at 231 cubic inches, ale at 282 and corn at about 268.8. The 1824 reform replaced them with the imperial gallon, defined as the volume of ten pounds of distilled water, calculated at 277.274 cubic inches. A new definition in 1889 slightly changed that, and after the liter was restored to exactly a cubic decimeter in 1964, Canada and then the UK in 1976 adopted the exact value of 4.54609 liters.

Because the United States kept the 231-cubic-inch wine gallon, an imperial gallon is about 20 percent larger than a US gallon. That explains why a car rated at 40 miles per gallon in Britain is less impressive in American terms, since it comes to roughly 33 US miles per gallon. Ireland dropped the gallon as a primary trade unit at the end of 1993 and the UK at the end of September 1995, but it lives on in British fuel-economy figures and older recipes.

Sources: Wikipedia: Gallon; UK Weights and Measures Act 1985, Schedule 1

Imperial Gallon conversion chart

1 imperial gallon expressed in every other volume unit:

More Imperial (British) units

• imperial quart (volume)
• imperial pint (volume)
• imperial gill (volume)
• imperial fluid ounce (volume)
• UK beer barrel (volume)
• firkin (volume)
• kilderkin (volume)
• hogshead (ale) (volume)
• stone (weight & mass)
• long ton (weight & mass)
• hundredweight (UK) (weight & mass)
• quarter (UK) (weight & mass)
• fortnight (time)
• score (time)
• furlong per fortnight (speed)
• poundal (force)

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