ConverterHub

US gallons to Imperial gallons Converter

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

How it is calculated

The tool multiplies the US gallon figure by two fixed factors: imperial gallons = US gallons × 0.832674 and litres = US gallons × 3.785411784. The second factor is the exact legal definition of the US gallon; the first is the ratio of 3.785411784 to 4.54609 litres, rounded to six decimals. Results are shown to four decimals, and the imperial figure is labelled "gal". The conversion works on volume of liquid only. Any number is accepted, including decimals, and the tool does not check the sign. Dry gallons, used for grain in older US measures, are a different volume and are not covered.

Worked example

A motorhome has a 15 US gallon fuel tank, and the UK brochure lists capacity in imperial gallons. Step 1: imperial gallons = 15 × 0.832674 = 12.49011. Step 2: litres = 15 × 3.785411784 = 56.78118. The tool shows 12.4901 gal and 56.7812 L. The same tank therefore holds about 12.5 imperial gallons, a figure about one sixth lower than the US number.

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Common mistakes

  • Multiplying by 1.2 instead of 0.8327 when going from US to imperial gallons; the imperial gallon is the larger unit, so the number gets smaller.
  • Comparing fuel economy in miles per gallon without checking which gallon is used: a car rated at 40 mpg (imperial) is only about 33 mpg (US).
  • Assuming a plain "gallon" in a Canadian or British spec is the US one; the label may mean imperial.
  • Reading the result in the "gal" line as US gallons again; here it is the imperial gallon.
  • Rounding the result before using it for tank sizing, which adds up on large volumes.

About this calculator

The US gallon (3.78541 litres) and the imperial (UK) gallon (4.54609 litres) are two genuinely different volumes that happen to share a name — the imperial gallon is about 20% larger, so 1 US gallon equals roughly 0.8327 imperial gallons. The split dates to 1824, when Britain redefined its gallon based on the volume of 10 pounds of water while the US kept using the older English wine gallon.

Engineers sizing fuel tanks and water systems for equipment sold in both the US and UK/Commonwealth markets, and travelers or importers reading a car's or appliance's fuel/water capacity spec, need this conversion specifically because "gallon" alone is ambiguous without knowing which country's standard is meant.

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