Fuel is sold by the liter in most countries and by the gallon in the United States and a few others. The UK uses liters at the pump today but historical fuel economy ratings still reference Imperial gallons. This converter handles all three: US gallons, Imperial (UK) gallons, and liters.
- 1 US gallon = exactly 3.785411784 liters (NIST SP 811)
- 1 Imperial gallon = exactly 4.54609 liters (UK Weights and Measures Act 1985)
The formula
liters = US gallons × 3.785411784
liters = Imperial gallons × 4.54609
US gallons = liters / 3.785411784
Imperial gal = liters / 4.54609
Practical examples
Example 1 — Filling a US rental car
A US rental car has a 15-gallon tank. You are in Europe and pay per liter.
15 US gal × 3.785411784 = 56.78 liters
At €1.80/L: 56.78 × 1.80 = €102.20 to fill the tank
Example 2 — UK car in the US
A UK-specification car has a 55-liter tank. A US owner wants to know in gallons.
55 ÷ 3.785411784 = 14.53 US gallons
Example 3 — Comparing fuel cost per Imperial gallon
UK fuel is priced at £1.55/L. Per Imperial gallon: 1.55 × 4.54609 = £7.05/Imperial gallon
Common mistakes
Assuming all gallons are equal. A US gallon is 3.785 L; an Imperial gallon is 4.546 L — about 20% larger. Car manuals from UK-market vehicles state tank capacity in liters, but older UK mpg figures used Imperial gallons.
Mixing up the gallon in mpg calculations. If you convert UK mpg to L/100km using the US gallon factor (3.785), you get a result that is ~20% too high. UK mpg uses the Imperial gallon (4.546 L). The fuel economy converter on this site uses US gallons — note this when comparing UK-sourced mpg figures.
Using approximate factors. 1 US gallon ≈ 3.8 L is commonly cited, but the exact value 3.785411784 is needed for precise fuel cost calculations or tank calibration.
International and regional variations
| Country | Fuel unit at pump | Gallon type (if used) |
|---|---|---|
| United States | US gallon | US (3.785 L) |
| United Kingdom | Liter (at pump since 1980s) | Imperial (4.546 L) in older mpg ratings |
| Canada | Liter | — |
| Most of Europe | Liter | — |
| Mexico | Liter | — |
Quick reference — common fuel volumes
| US Gallons | Liters | Imperial Gallons |
|---|---|---|
| 1 | 3.785 | 0.833 |
| 5 | 18.93 | 4.163 |
| 10 | 37.85 | 8.327 |
| 15 | 56.78 | 12.49 |
| 20 | 75.71 | 16.65 |
| 50 | 189.3 | 41.63 |