Explainer
What Is a Gallon?
Understanding the gallon, including the difference between US and Imperial gallons.
Last updated: 2026-03-15
US vs Imperial Gallons
| Property | US Gallon | Imperial Gallon |
|---|---|---|
| Liters | 3.785 | 4.546 |
| Fluid ounces | 128 (US) | 160 (Imp) |
| Quarts | 4 | 4 |
| Pints | 8 | 8 |
| Cubic inches | 231 | 277.42 |
Where Each Is Used
- US gallon: United States, some Caribbean and Latin American countries
- Imperial gallon: UK (historically), Canada (historically), some Commonwealth nations
- Note: Canada and the UK have largely switched to liters for most purposes, but "gallon" references in those countries typically mean Imperial gallons
Common Gallon Uses
| Item | US Gallons | Liters |
|---|---|---|
| Milk jug | 1 | 3.785 |
| Car fuel tank | 12-16 | 45-60 |
| Standard bathtub | 80 | 303 |
| Swimming pool (avg) | 20,000 | 75,708 |
| Daily water per person | ~80 | ~303 |
History
The word "gallon" comes from Old French "galon." Before standardization, there were many different gallons: the wine gallon, ale gallon, corn gallon, and more. The US adopted the wine gallon (231 in³) while Britain created the Imperial gallon (277.42 in³) in 1824.
Fuel Economy Note
When comparing fuel economy between US and UK vehicles, remember that Imperial gallons are 20% larger. A car getting 30 mpg (US) would get about 36 mpg (Imperial). Most of the world uses liters per 100 km instead.
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