ConverterHub

Imperial gallons to US gallons Converter

Enter a value in imperial gallons to convert it to us gallons, litres.

Result

12.0095 gal
45.4609 L

How it is calculated

The tool multiplies the number of imperial gallons by a fixed factor: US gallons = imperial gallons × 1.20095042. The factor is the ratio of the two gallons, 4.54609 L divided by 3.785411784 L. It also gives the volume in litres with litres = imperial gallons × 4.54609. Both results are shown to four decimals with their units. There is no rounding of the input and no limit on its size; the tool accepts any number, so use positive volumes. To go the other way, divide US gallons by 1.20095042. Only volume is converted. Fuel-economy figures are the reverse: a rating in miles per imperial gallon becomes a smaller number in miles per US gallon.

Worked example

A boat fuel tank holds 10 imperial gallons. US gallons = 10 × 1.20095042 = 12.0095 gal. Litres = 10 × 4.54609 = 45.4609 L. So the same tank is about 20% larger when counted in US gallons, because each US gallon is a smaller volume. If a car does 40 miles per imperial gallon, dividing by 1.20095 gives about 33.3 miles per US gallon for the same car.

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Common mistakes

  • Treating the two gallons as equal. A US gallon is about 17% smaller than an imperial gallon, so a tank's capacity differs by about a fifth between the two systems.
  • Multiplying when you should divide, or the reverse. Imperial to US gives a bigger number; US to imperial gives a smaller one.
  • Comparing fuel economy in mpg between UK and US sources without converting. A UK 40 mpg is about 33.3 mpg by US measure.
  • Assuming the label "gallon" in a Canadian or UK recipe or spec means a US gallon. Check which one the source uses.
  • Confusing gallons with litres when reading the result. The tool shows both, so make sure you take the one with the unit you need.

About this calculator

The imperial gallon (used in the UK, Canada, and historically the Commonwealth) and the US gallon are different volumes despite sharing a name: 1 imperial gallon = 4.54609 litres, while 1 US gallon = 3.78541 litres, making 1 imperial gallon ≈ 1.20095 US gallons. The imperial gallon was originally defined as the volume of 10 pounds of water; the US gallon derives from an older English wine gallon.

The mismatch matters most in fuel economy figures — a car rated at 40 mpg in the UK is not achieving 40 mpg by US standards, since the same distance is being divided by a larger gallon — as well as in recipe conversion, fuel tank capacities, and any cross-border trade in liquids where UK/Canadian and US specifications are quoted in "gallons" without clarifying which one.

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