Guide
US Gallon vs Imperial Gallon: What Is the Difference?
US gallons and UK imperial gallons are not the same. Learn the sizes, where each is used, and how to convert gallons to liters correctly.
4 min read
Not all gallons are equal
The US liquid gallon equals 3.78541 liters. The UK imperial gallon equals 4.54609 liters — about 20% larger. Mixing them up when fueling, cooking, or reading specs can lead to significant errors.
ConvertHub uses US customary units for gallon, quart, pint, cup, and fluid ounce unless stated otherwise — matching American labels and most online US recipes.
Where each gallon appears
US gallon: fuel pumps in the United States, US milk jugs, American beer keg sizing references, EPA fuel-economy figures (miles per gallon).
Imperial gallon: fuel economy in the United Kingdom and Canada (historically), some Commonwealth countries. UK fuel prices are often quoted per liter today, but older literature still references imperial gallons.
Conversion cheat sheet
Use these rounded values for quick checks:
- 1 US gallon ≈ 3.79 liters
- 1 imperial gallon ≈ 4.55 liters
- 1 US gallon ≈ 0.83 imperial gallons
- 4 liters ≈ 1.06 US gallons
- 1 US quart = 0.946 liters
Avoiding mistakes
When a recipe or manual says "gallon," check the country of origin. British baking books may assume imperial pints and gallons.
For fuel economy: US mpg and UK mpg are not comparable without converting the underlying gallon definition. Always convert to liters per 100 km for a fair comparison.