How many litres are in a gallon? US and imperial gallons differ
The word gallon can refer to different volumes. Confirm the definition before comparing fuel economy, storage capacity or product quantities.
Unit converter →Compare the two definitions
One US liquid gallon equals 3.785411784 litres, while one imperial gallon equals 4.54609 litres. Ten gallons therefore represent about 37.854 litres or 45.461 litres respectively, a difference of roughly 7.607 litres. A number labeled only gal leaves an important ambiguity that arithmetic cannot resolve on its own.
Be especially careful with fuel economy
A figure of 40 miles per gallon represents different consumption depending on which gallon is used. Convert the distance and volume consistently before comparing two records. In the volume category, this site distinguishes US gal from imp gal rather than treating the labels as interchangeable. The conversion factor belongs to the unit definition, not the language of the page.
Check the original source of the measurement
Product specifications, vehicle information and historical records may use different conventions. Read the original unit note instead of guessing from the country or wording alone. The fuel calculator expects litres and kilometres, so convert the underlying quantities before entering them; it does not directly parse an mpg label. Keep the gallon type with any saved result so another person can reproduce the conversion without repeating the ambiguity.
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