🔁 Conversion
Converting Litres to Gallons (and Why US and Imperial Differ)
Convert between litres, gallons, cups and fluid ounces — and understand why a US gallon and an imperial gallon are not the same size.
Updated 12 October 2026 · 2 min read
Volume is where the metric and imperial worlds collide most awkwardly. A litre is a litre everywhere, but the word "gallon" means two different things depending on which side of the Atlantic you're on — and that single fact is behind most volume-conversion mistakes.
The key conversion factors
To go from litres to US gallons, divide by 3.785; for imperial gallons, divide by 4.546. Going the other way, multiply. So 10 litres is 10 ÷ 3.785 ≈ 2.64 US gallons, but only 10 ÷ 4.546 ≈ 2.20 imperial gallons.
Why the two gallons differ
The imperial gallon was defined in the UK as the volume of ten pounds of water, which works out to 4.546 litres. The US gallon descends from an older English wine gallon of 231 cubic inches, or 3.785 litres. Neither was wrong — they simply froze different historical standards into law. The gap carries down into every smaller unit: a US pint is 16 fluid ounces, an imperial pint is 20.
Cups, pints and fluid ounces
- A US cup is about 237 ml; a "metric cup" used in some recipes is a round 250 ml.
- A US fluid ounce is about 29.6 ml, while an imperial fluid ounce is 28.4 ml — close, but not identical.
- A US pint (473 ml) is smaller than an imperial pint (568 ml), which is why a British pint of beer feels more generous.
- Millilitres are the safest unit for recipes, because they mean exactly the same thing in every country.
Converting without the mix-ups
The reliable approach is to always note *which* gallon, cup or pint a figure refers to before you convert. The volume converter lists US and imperial units separately for exactly this reason, so you never accidentally mix a US gallon with an imperial pint. For the broader picture of why these two systems exist side by side, see metric vs imperial, and for kitchen-specific swaps there's the guide to cooking conversions.
Frequently asked questions
- How many litres are in a gallon?
- It depends on the gallon. A US gallon is 3.785 litres and an imperial (UK) gallon is 4.546 litres, so the imperial gallon is roughly 20% larger.
- Why is a US gallon smaller than an imperial gallon?
- They come from different historical standards. The US gallon kept an old English wine gallon of 231 cubic inches (3.785 litres), while the UK later redefined the imperial gallon as ten pounds of water (4.546 litres).
- Should I use millilitres or cups for recipes?
- Millilitres are the most reliable because they mean the same thing everywhere. A "cup" can be a US cup (237 ml) or a metric cup (250 ml), so converting to millilitres removes the ambiguity.