The exact answer (both gallons)

Volume converts cleanly, so the numbers are fixed:

1 litre = 0.264 US gallons (because 1 US gallon = 3.785 litres).
1 litre = 0.220 imperial gallons (because 1 UK gallon = 4.546 litres).

Here’s the thing most people are really after: because a litre is the smaller unit, “gallons in a litre” always comes out as a fraction. If you’re trying to fill a gallon jug or read an American recipe, you probably want it the other way round — a US gallon is about 3.79 litres, a UK gallon about 4.55 litres. And “a litre of water” is no different from a litre of anything else: this is pure volume, so the substance doesn’t change the conversion.

The trap: US gallon vs UK gallon

The single biggest source of confusion is that there are two different gallons, and they aren’t close. The US gallon is 3.785 litres; the imperial (UK) gallon is 4.546 litres — about 20% larger. So the same litre figure gives noticeably different gallon answers depending on which side of the Atlantic you mean.

This quietly wrecks comparisons. A car rated “40 miles per gallon” in Britain isn’t as efficient as “40 MPG” in the US, because the British gallon holds more fuel. Canada adds one more wrinkle: it’s officially metric and sells fuel by the litre, but the old “Canadian gallon” was the imperial one (4.546 litres), so vintage references can mean either.

For any value not in the table, the converter handles it instantly.

Why does anyone ask this?

It’s a strangely popular question for such a small number, and the reasons are nearly always practical:

Fuel prices. Most of the world prices petrol per litre; the United States prices it per gallon. Travellers, importers and car-forum regulars convert constantly to compare. A pump price of $1.40 a litre, for instance, works out to about $5.30 a US gallon — or $6.36 an imperial gallon. The headline number changes dramatically depending on the unit, which is exactly why people check.

Fuel economy. The same divide shows up in efficiency: the US and UK quote miles per gallon, most other countries quote litres per 100 km. Converting between them means juggling both miles-to-kilometres and litres-to-gallons at once.

Tanks and containers. A “60 litre tank” (about 15.8 US / 13.2 UK gallons) might be a fuel tank, a water butt or a fish tank — aquarium stocking rules are often written in gallons, so metric fishkeepers convert to follow them.

Recipes and travel. Older American recipes, paint coverage, and equipment specs all turn up in gallons, while the rest of the world buys in litres. Anyone moving between the two systems ends up doing this conversion sooner or later.

One thing it’s not: engine size

A surprising number of searches ask how many gallons are in a “2 litre engine” (or 1.4, or 1.2). It’s a natural question, but there’s nothing to convert. An engine’s “litres” describe its displacement — the total swept volume of all its cylinders — not how much fuel it holds. A 2-litre engine doesn’t carry two litres of anything; the figure is just a size label. Turning it into gallons (about 0.53 US gallons) is a real number, but a meaningless one for anything you’d actually do with a car.

Quick mental-maths tricks

For rough conversions in your head: to go from litres to US gallons, multiply by about 0.26 (or divide by ~3.8) — close to “a quarter.” For UK gallons, multiply by about 0.22 (or divide by ~4.5) — a bit over a fifth. Going the other way, multiply gallons by 3.8 (US) or 4.5 (UK) to get litres. For anything where the decimals matter, though, it’s faster and safer to let the converter do it.

Common questions

Sources

• NIST / international definitions — 1 US gallon = 3.785411784 L; 1 imperial gallon = 4.54609 L.
• Derived conversions — 1 L = 0.264172 US gal = 0.219969 UK gal.

Related