Imperial Gallons to US Gallons (gal (UK) to gal)

1 imperial gallon equals 1.200949926 US gallons (rounded).

1 imperial gallon = 1.200949926 US gallons

How to convert imperial gallons to US gallons

To convert imperial gallons to US gallons, multiply the number of imperial gallons by 1.200949926. The factor is rounded to 10 significant digits. To go the other way, multiply US gallons by 0.8326741846 (rounded).

US gallons = imperial gallons × 1.200949926

Example: 10 imperial gallons = 12.00949926 US gallons.

Pints, quarts, gallons and fluid ounces differ between the US and the UK. Units are labeled 'US' or 'imperial' to avoid confusion.

About these units

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.

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.

1 imperial gallon = 4.54609 liters (exactly).

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

US Gallon (gal)

US customaryCurrent unit

Exactly 231 cubic inches or 3.785411784 liters (128 US fluid ounces). About 17% smaller than the imperial gallon.

The US gallon is a survivor of English wine trade. Around 1706, a statute in Queen Anne's reign fixed the wine gallon at exactly 231 cubic inches, settling confusion among the competing gallons for wine, ale and corn. British colonies in North America used that wine gallon, and in 1824 Britain replaced all its gallons with a new imperial one while the United States kept the old measure. It was adopted as the legal US standard in 1836 and is still defined as exactly 231 cubic inches, or 3.785411784 liters.

That makes the US gallon about 17 percent smaller than the imperial gallon, a difference that explains why American and British fuel-economy figures cannot be compared directly. Everyday uses are milk jugs, paint cans and gasoline pumps. One gallon divides evenly into four quarts, eight pints, sixteen cups and 128 fluid ounces. A gallon of water weighs a little over 8 pounds, an easy figure to remember when loading a car with water jugs.

1 US gallon = 3.785411784 liters (exactly).

Sources: Wikipedia: Gallon; NIST SP 811, Appendix B.8: conversion factors for volume

Related conversions

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