Litres and gallons — reading fuel tank capacities without surprises
1 US gallon = 3.785 L. 1 UK gallon = 4.546 L. The 20% gap is the same one that ruins fuel-economy comparisons.
The US gallon and the UK (Imperial) gallon share a name and nothing else. A 15-gallon fuel tank on a US pickup holds 56.8 L; the same-sized tank on a UK van rated 15 (Imperial) gallons holds 68.2 L. The 20% difference has caught out fleet managers, importers and every backpacker filling up abroad.
The exact factors
1 US gallon = 3.785411784 L (exact) > 1 Imperial gallon = 4.54609 L (exact) > 1 US gal = 0.8327 UK gal > 1 L = 0.2642 US gal = 0.2200 UK gal
Regional labelling conventions
US: gallons everywhere. UK: litres at the pump, gallons in casual fuel-economy talk. Canada: litres exclusively since 1979. Australia: litres. EU: litres. Japan: litres. Only the US retains gallons on the pump.
Worked example — a 60 L rental car in the US
You land in Los Angeles, rent a car with a 60 L tank (16 US gal) and fill up in Nevada for $3.50/gal. 60 L / 3.785 = 15.85 US gal × $3.50 = $55.48. If the same tank were labelled in UK gal you would expect 60/4.546 = 13.2 gal — the mismatch of 2.65 gal at $3.50 is $9.28 you did not budget.
Boat and aircraft fuel
Marine and aviation fuel is often quoted in US gallons regardless of country, because the industry standardised on US convention. A 100-gallon aviation fuel order in the UK is 378.5 L, not 454.6 L. Always confirm at the fuel truck.
The five-second recap
Multiply US gal by 3.785 for L. Multiply UK gal by 4.546 for L. The two gallons differ by 20%. Aviation defaults to US gal worldwide.
Try the converters mentioned in this article
FAQ
Which gallon is the US gallon based on?+
The Queen Anne wine gallon of 1707 — 231 cubic inches exactly. The UK abandoned it in 1824 for the Imperial gallon; the US kept it.
How many litres in a barrel of oil?+
1 US oil barrel = 158.987 L = 42 US gal. This is different from a US liquid barrel (119.24 L) or a UK beer barrel (163.66 L).
Does Canada use US or UK gallons?+
Neither in practice — Canada switched to litres in 1979. Legacy references are UK gallons (a Canadian 'gallon' historically = 4.546 L).
This article was written by The Turbo Unit Converter engineering desk (Automotive metrology) and last reviewed on 2026-06-28 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.