US Gallon vs UK Gallon: How to Convert Litres to Gallons

The short answer

A US gallon is 3.785 litres and a UK (imperial) gallon is 4.546 litres, so a UK gallon is about 20% bigger. To convert litres to gallons, divide by 3.785 for US gallons or by 4.546 for UK gallons: 50 litres is 13.21 US gallons or 11.00 UK gallons. The Volume Converter has both US Gallon and UK Gallon options.

Two gallons with the same name

The two gallons are defined differently:

• US gallon: legally defined as exactly 231 cubic inches, which is 3.785411784 litres. Used in the United States and some other countries for fuel and liquids.
• Imperial (UK) gallon: defined as exactly 4.54609 litres. Used in the United Kingdom, where fuel economy is still commonly quoted in miles per gallon even though fuel is sold by the litre.

| US gallon	UK gallon
Litres	3.785	4.546
In the other gallon	0.833 UK gallons	1.201 US gallons
US fluid ounces	128	about 154

Conversion examples

All values below are from the Volume Converter.

Litres	US gallons	UK gallons
1 L	0.264	0.220
20 L	5.28	4.40
50 L	13.21	11.00
100 L	26.42	22.00
Gallons	US gallons in litres	UK gallons in litres
1	3.79 L	4.55 L
5	18.93 L	22.73 L
10	37.85 L	45.46 L

Note that the converter stores the US gallon as 3.78541 litres, so results match the exact definition to five decimal places, which is far more precise than any real measurement of fuel or water.

How to convert in the tool

Open the Volume Converter.

Enter the amount.

Set From to Liter (L), US Gallon or UK Gallon.

Choose the target unit. The table underneath shows every unit at once, so you can see US and UK gallons side by side.

Use the swap button (⇄) to reverse the direction; the current result becomes the new input.

How to tell which gallon is meant

• American products, recipes, car specs and fuel prices: US gallon.
• UK car brochures, older British recipes and UK mpg figures: imperial gallon.
• Fish tanks, paint and garden sprayers: check the label. Many show litres too, which removes the doubt.
• Online content without a country: look for spelling (litre or liter), currency and other units. If you cannot tell, convert both and see which number makes sense.

The pint follows the same split: a US pint is about 473 ml and a UK pint about 568 ml. The tool's pint and quart options are US measures.

Miles per gallon: the mix-up that matters most

Because the gallons differ, the same car has two different mpg figures:

• 30 mpg (US) = about 36 mpg (UK). The UK number is higher because each UK gallon contains more fuel.

So a car advertised in the UK at 45 mpg is not more efficient than an American car rated at 40 mpg until you convert them to the same gallon. The cleanest comparison is to use a metric figure such as km/L or L/100 km.

For fuel economy, use the dedicated Fuel Efficiency Converter, which has separate US and UK mpg options as well as km/L and L/100 km. The guide to converting km/L to L/100 km and mpg explains why these units work differently.

km/L	mpg (US)	mpg (UK)
15 km/L	35.3	42.4

Worked examples

A car fuel tank. A tank listed as 12 US gallons holds 12 × 3.785 = 45.4 litres. If the same figure were 12 UK gallons, the tank would hold 54.6 litres, about 9 litres more. Always check which gallon a spec sheet means before planning a trip or comparing cars.

A water tank. A 1,000-litre tank is 264.2 US gallons or 220.0 UK gallons. One cubic metre is the same 1,000 litres, so the converter's m³ option gives the same results.

A paint tin. A 5 US gallon bucket is 18.9 litres. If a project needs 20 litres, one bucket is not quite enough.

In each case, convert to litres first when two sources use different gallons. Litres are the same everywhere, so they make a safe common unit.

Common mistakes

Assuming one gallon is 4 litres

It is a handy rough guess for a US gallon (3.79 L), but it understates a UK gallon by more than half a litre. For a 40-gallon UK tank, using 4 litres instead of 4.546 gives a total that is about 22 litres short.

Mixing gallons in one calculation

If a tank's capacity is in UK gallons and the fuel price is per US gallon, convert both to litres first, then do the maths.

Rounding too early

Convert first, then round the final answer. Rounding 3.785 to 4 at the start, then multiplying by a large number, magnifies the error.

Related conversions

• For cooking volumes, see how many ml are in a cup.
• For cubic metres, the converter shows that 1 m³ is 1,000 litres, or about 264 US gallons, which is useful for water tanks.
• For an overview of other units, read the unit conversion guide.