Litres to Gallons Calculator

How to use this calculator

1. Enter the value you haveLitres from a fuel receipt, a tank capacity or a service schedule; gallons from an older manual or an American source.
2. Pick the directionThe dropdown switches between litres to gallons and gallons to litres. The factor is applied or divided accordingly.
3. Check which gallon you actually meanThis calculator uses the UK imperial gallon at 4.54609 litres. If your source is American, the number is 3.78541 and everything downstream will differ by about 17 per cent.
4. Use the quick reference rowsThe breakdown converts several common values at once, which is faster than re-entering figures one at a time.

How the calculation works

The conversion is a single multiplication and the only complication is which gallon you mean.

The imperial gallon was originally defined as the volume of ten pounds of water at a specified temperature, and since 1985 it has been defined exactly as 4.54609 litres. Dividing litres by that figure gives imperial gallons; multiplying gallons by it gives litres.

The US liquid gallon derives from a completely different historical standard — the English wine gallon of 231 cubic inches — and works out at 3.785411784 litres. The two were never the same measure and the difference is not a rounding artefact.

That 17 per cent gap is the source of almost every gallon-related error. American fuel economy figures quoted in miles per gallon look considerably worse than they are when read as imperial, and a UK figure quoted to an American audience looks flattering. Any cross-Atlantic comparison of fuel economy that does not state which gallon is being used is not comparable.

Quick reference

A useful mental shortcut: one imperial gallon is a little over four and a half litres, so dividing litres by 4.5 gets you within about one per cent. For US gallons, dividing by 3.8 does the same job.

Why the UK uses both at once

Britain sits in an unusual position of measuring fuel in litres and fuel economy in miles per gallon. Fuel has been sold by the litre since the late 1980s, but efficiency is still quoted in mpg by manufacturers, motoring journalists and drivers alike.

That produces the everyday awkwardness this calculator exists for. You fill up with 48 litres, you know your car does 45 mpg, and comparing the two requires a conversion before either number is useful.

The practical conversion most people actually want is litres per 100 kilometres to miles per gallon, which is the metric the rest of Europe uses. That relationship is inverse rather than linear — as one rises the other falls — so it cannot be done with a single multiplication. The constant, for the imperial gallon, is 282.5: divide 282.5 by the litres per 100 km figure to get mpg, and divide it back to reverse.

So a car quoted at 5.5 l/100km does 282.5 ÷ 5.5 = 51.4 mpg. Using the US constant of 235.2 instead would give 42.8 mpg — the same car, apparently 17 per cent thirstier.

Assumptions and limitations

• Uses the UK imperial gallon at exactly 4.54609 litres
• Does not convert to or from the US liquid gallon, which is 3.785411784 litres
• Does not handle the US dry gallon, a separate and rarely used measure
• Assumes liquid volume — converting a weight to a volume needs the substance's density
• Results are shown to four decimal places, which is far beyond practical precision for fuel
• Does not convert fuel economy units, which is an inverse rather than linear relationship

Questions people ask about this in United Kingdom