Which gallon? US and imperial differ by 20%
The word "gallon" means two different sizes. In the US it is 3.785 litres; in the UK and much of the Commonwealth it is the imperial gallon of 4.546 litres. Mixing them up when buying fuel or pool chemicals is a real error, not rounding.
The imperial gallon holds 0.761 L more than the US gallon — the same word for two containers that differ by about a fifth.
The exact factors
For a rough US figure, treat a gallon as "almost 4 litres" and a litre as "just over a quarter gallon." A 4-litre jug is nearly, but not quite, one US gallon.
Litres to gallons, both systems
| Litres | US gallons | Imperial gallons |
|---|---|---|
| 1 | 0.264 | 0.220 |
| 5 | 1.321 | 1.100 |
| 10 | 2.642 | 2.200 |
| 20 | 5.283 | 4.399 |
| 40 | 10.567 | 8.799 |
| 60 | 15.850 | 13.199 |
| 100 | 26.417 | 21.997 |
A "5-gallon bucket" in the US holds 18.93 L; five imperial gallons would be 22.73 L.
Where the difference bites
- Fuel economy. US MPG and UK MPG aren't comparable — the UK figure looks better only because the gallon is larger. To go metric, divide 235.21 by US MPG (or 282.48 by imperial MPG) for litres per 100 km.
- Fluid ounces don't match either. A US gallon is 128 US fl oz; an imperial gallon is 160 imperial fl oz. And a US fl oz (29.57 mL) is slightly larger than a UK one (28.41 mL).
- Dry gallon exists too. The US also has a dry gallon (4.405 L) for produce and grain. It's separate from the liquid gallon on this page.
Common questions
How many litres are in a gallon?
A US gallon is 3.785 litres. An imperial (UK) gallon is 4.546 litres, about 20% larger. Always check which gallon you mean.
How many gallons is one litre?
One litre is 0.2642 US gallons, a little over a quarter of a gallon. In imperial gallons it is 0.2200.
Why are US and UK gallons different?
The US kept the old English wine gallon of 231 cubic inches, while Britain redefined its gallon in 1824 as the volume of 10 pounds of water. The two definitions were never reconciled, leaving a 20% gap.
Is 4 litres the same as a gallon?
Almost, for a US gallon. 4 litres is 1.057 US gallons, so a 4-litre container is about 5.7% more than one US gallon. It is well short of an imperial gallon.
