US Gallon vs Imperial Gallon
Last updated February 14, 2026 · Volume
The word 'gallon' means two different volumes depending on where you are. The US liquid gallon is exactly 3.785411784 litres. The Imperial gallon, used in the United Kingdom and historically in Canada, Australia and New Zealand, is exactly 4.54609 litres — roughly 20.1% larger.
Why they differ
The US gallon descends from the English wine gallon of 231 cubic inches, fixed before American independence. Britain redefined its gallon in 1824 as the volume of ten pounds of water at 62 °F, producing the larger Imperial gallon. The United States never adopted the change.
The knock-on effects
- 1 US gallon = 128 US fluid ounces; 1 Imperial gallon = 160 Imperial fluid ounces
- A US pint is 16 US fl oz (473 mL); an Imperial pint is 20 imp fl oz (568 mL)
- A US fluid ounce (29.57 mL) is slightly larger than an Imperial fluid ounce (28.41 mL)
- Fuel economy figures do not transfer: 40 Imperial MPG is about 33.3 US MPG
Quick comparison
| Measure | Volume |
|---|---|
| US liquid gallon | 3.785411784 L |
| Imperial gallon | 4.54609 L |
| US liquid pint | 473.176 mL |
| Imperial pint | 568.261 mL |
| US fluid ounce | 29.5735 mL |
| Imperial fluid ounce | 28.4131 mL |
Which one do you need?
If the figure comes from a US source — a recipe, a fuel price, a car spec sheet — use the US gallon. If it comes from the UK, or from an older Canadian, Australian or New Zealand source, use the Imperial gallon. Modern Canadian, Australian and New Zealand fuel figures are given in litres or L/100 km instead.