Quick answer: A UK (imperial) gallon is 4.54609 litres and a US gallon is 3.785411784 litres, so the UK gallon is about 20% bigger. One UK gallon equals 1.20095 US gallons, and one US gallon equals 0.83267 UK gallons. The same gap makes UK miles-per-gallon figures look higher than American ones.
Both countries call their unit a gallon, both split it into 8 pints, and yet they differ by more than three quarters of a litre. That matters whenever you follow an American recipe or brewing kit, read a US car review or compare fuel economy. Use the converters below, then read on for the formula, a printable chart and the history. For the wider context of imperial units in Britain, see our guide to the UK measurement system.
UK gallons to US gallons and litres
UK gal= US gal= litresUS gallons to UK gallons and litres
US gal= UK gal= litresUK mpg to US mpg and litres per 100 km
UK mpg= US mpg= L/100 kmHow much bigger is a UK gallon than a US gallon?
A UK gallon is 0.761 litres, or about 20.1%, bigger than a US gallon. Dividing 4.54609 by 3.785411784 gives 1.20095, so one UK gallon equals 1.20095 US gallons. Going the other way, one US gallon equals 0.83267 UK gallons, or roughly five-sixths of an imperial gallon.
The formulas are:
- US gallons = UK gallons × 1.20095
- UK gallons = US gallons × 0.83267
- Litres = UK gallons × 4.54609, or US gallons × 3.78541
Worked example: an American home-brew kit makes 5 US gallons of beer. That is 5 × 3.78541 = 18.93 litres, or 5 × 0.83267 = 4.16 UK gallons. In UK pints, 18.93 litres ÷ 0.568 = about 33 pints, not the 40 pints you might expect from 5 imperial gallons. For straightforward litre conversions, use the litres to gallons converter.
UK and US gallons conversion chart
This chart gives both gallons in litres, plus the cross-conversion, rounded sensibly. Print it or save it for reference.
| Gallons | UK gallons in litres | US gallons in litres | UK gallons in US gallons | US gallons in UK gallons |
|---|---|---|---|---|
| 1 | 4.55 L | 3.79 L | 1.201 | 0.833 |
| 2 | 9.09 L | 7.57 L | 2.402 | 1.665 |
| 3 | 13.64 L | 11.36 L | 3.603 | 2.498 |
| 4 | 18.18 L | 15.14 L | 4.804 | 3.331 |
| 5 | 22.73 L | 18.93 L | 6.005 | 4.163 |
| 10 | 45.46 L | 37.85 L | 12.009 | 8.327 |
| 20 | 90.92 L | 75.71 L | 24.019 | 16.653 |
| 50 | 227.30 L | 189.27 L | 60.047 | 41.634 |
| 100 | 454.61 L | 378.54 L | 120.095 | 83.267 |
Why are UK and US gallons different?
The two countries standardised on different old English gallons. Before 1824 England had several gallons for different goods. The United States adopted the old wine gallon of 231 cubic inches, which is still the definition of the US liquid gallon. Britain went the other way: the Weights and Measures Act 1824 created a new imperial gallon, defined as the volume of 10 pounds of distilled water under set conditions, for all liquids and dry goods.
Both have since been fixed in metric terms. UK law now defines the gallon as exactly 4.54609 cubic decimetres (litres), while 231 cubic inches works out at exactly 3.785411784 litres because the inch is exactly 25.4 mm. The pints follow the gallons: a UK pint is 568 ml and a US pint 473 ml, as explained in our guide to the size of a UK pint of beer.
Why do UK and US mpg figures differ?
Because a UK gallon holds more fuel, the same car travels further on it, so UK mpg figures are about 20% higher than US ones. A car that does 50 mpg in UK terms does 41.6 mpg in US terms, with no difference in actual efficiency. To convert, multiply UK mpg by 0.83267, or divide US mpg by 0.83267 to go the other way.
| UK mpg | US mpg | Litres per 100 km |
|---|---|---|
| 30 | 25.0 | 9.42 |
| 40 | 33.3 | 7.06 |
| 45 | 37.5 | 6.28 |
| 50 | 41.6 | 5.65 |
| 60 | 50.0 | 4.71 |
| 70 | 58.3 | 4.04 |
The litres per 100 km column uses the formula 282.48 ÷ UK mpg, which comes from 100 × 4.54609 ÷ 1.609344. Bear this in mind when reading American car reviews or forums: a US figure will always look worse than the same car's UK figure.
Where is the gallon still used in the UK?
Mainly in fuel economy, where miles per gallon remains the everyday measure even though fuel is sold by the litre. UK petrol pumps moved to litres by the mid-1990s, so drivers now buy fuel in one unit and judge economy in another. The gallon also lingers informally for water butts, ponds and aquariums, home brewing and older recipes.
In trade, the gallon is a supplementary unit only: a garden centre can label a water butt "200 litres (44 gallons)" but must give the litre figure, more prominently. The rules are explained in which imperial units are still legal in the UK. Related tools include the main volume converter and the ml to fl oz converter for smaller quantities.
Frequently asked questions
How many litres are in a UK gallon?
A UK (imperial) gallon is exactly 4.54609 litres. That is 8 UK pints or 160 UK fluid ounces.
How many litres are in a US gallon?
A US liquid gallon is exactly 3.785411784 litres, usually rounded to 3.785 litres. It is 8 US pints or 128 US fluid ounces.
Is a UK gallon bigger than a US gallon?
Yes. A UK gallon is about 20% bigger: 1 UK gallon equals 1.20095 US gallons, and 1 US gallon equals 0.83267 UK gallons.
How do I convert US mpg to UK mpg?
Multiply US mpg by 1.20095. For example, 40 US mpg is about 48 UK mpg. To go from UK to US mpg, multiply by 0.83267.
Does Canada use UK or US gallons?
Canada historically used the imperial gallon, the same as the UK, but it now sells fuel and most liquids in litres.
Sources
- Weights and Measures Act 1985, Schedule 1 (definition of the gallon), legislation.gov.uk
- NIST Guide to the SI, Appendix B: conversion factors, National Institute of Standards and Technology
- Choice on units of measurement: guidance on markings and sales, GOV.UK
- National Physical Laboratory, the UK's national measurement institute