The short answer
1 liter = 0.2641720524 US liquid gallons = 0.2199692483 imperial gallons.
US gallons = liters × 0.264172 (liters = US gal × 3.785411784)
UK gallons = liters × 0.219969 (liters = UK gal × 4.54609)The imperial gallon is about 20% larger than the US gallon. That single fact causes more conversion errors than any other in fluid measure.
Why two gallons exist
The US gallon was frozen at the old English wine gallon of 231 cubic inches (3.785411784 L exactly). Britain replaced its patchwork of gallons in 1824 with the imperial gallon, originally the volume of 10 lb of water, now defined as exactly 4.54609 L. Canada, the UK and several Caribbean nations use the imperial gallon; the US and most of Latin America use the US gallon.
Conversion chart
| Liters | US gallons | Imperial gallons |
|---|---|---|
| 1 L | 0.264 | 0.220 |
| 5 L | 1.321 | 1.100 |
| 10 L | 2.642 | 2.200 |
| 20 L | 5.283 | 4.399 |
| 50 L | 13.209 | 10.998 |
| 100 L | 26.417 | 21.997 |
| 208 L (drum) | 54.95 | 45.75 |
Fuel economy trap
Converting L/100 km to MPG is not a multiplication — it is a reciprocal:
MPG (US) = 235.215 ÷ (L/100 km)
MPG (UK) = 282.481 ÷ (L/100 km)A car at 8 L/100 km does 29.4 US MPG but 35.3 UK MPG. A "40 MPG" British car is only 33.3 US MPG — the same car, different gallon.
Smaller volume units
| Unit | Milliliters |
|---|---|
| US fluid ounce | 29.5735 mL |
| Imperial fluid ounce | 28.4131 mL |
| US cup (legal) | 240 mL |
| US customary cup | 236.588 mL |
| US pint | 473.176 mL |
| Imperial pint | 568.261 mL |
| US quart | 946.353 mL |
Note the inversion: the imperial gallon is bigger, but the imperial fluid ounce is smaller — because an imperial gallon splits into 160 fl oz while a US gallon splits into 128.
Practical cases
- Aquariums: a "55 gallon" US tank is 208 L; buying UK-rated equipment sized in imperial gallons oversizes flow by 20%.
- Recipes: a British pint of milk is 568 mL, an American pint 473 mL — a 20% overshoot in a batter.
- Chemical dosing: always convert to liters first, dose in mg/L, then convert back once.
Key takeaways
- US gal = 3.785411784 L; imperial gal = 4.54609 L, both exact
- Imperial gallons are ~20% larger; imperial fluid ounces are ~4% smaller
- Fuel economy converts by division (235.215 ÷ L/100 km), not multiplication
- State which gallon you mean in any technical document