Litres to Gallons Calculator

Litres to gallons: why the answer depends which gallon you mean

The litre is the metric unit of volume used across the UK for fuel, drinks, paint, and almost everything else sold by liquid measure. The gallon, by contrast, has two completely different legal definitions depending on where you are: the UK/imperial gallon is exactly 4.54609 litres, while the US gallon is exactly 3.785411784 litres — about 20% smaller. That's a big enough gap that using the wrong one gives a genuinely wrong answer, not just a slightly rounded one, which is exactly why this calculator shows both figures side by side rather than picking one.

Almost every "litres to gallons" search rooted in the UK means the imperial gallon — it's what UK fuel-tank capacities, historical mpg figures, and older UK product measurements are based on. But because so much online content, and every US-published source, uses the US gallon by default, it's easy to end up with a figure that's technically correct for the wrong country.

It's worth noting that the imperial gallon isn't just "the UK's gallon" in a loose sense — Ireland and several other former British territories historically used, and in some cases still officially recognise, the imperial gallon. Most of the world has since moved to litres for everyday retail regardless, which is why "gallon" today mainly survives as a specialist or historical reference: when a source simply says "gallon" without specifying which one, UK and Irish context should generally be read as imperial, while US-published figures should be read as the US gallon.

Quick conversions

Commonly searched litres-to-gallons figures, UK/imperial gallon:

Common litres to gallons conversions (UK vs US)

A comparison table from 10 to 200 litres, showing both the UK/imperial and US gallon figures:

Conversion formula and method

The formulas, using the exact legal definitions:

UK / imperial gallons = Litres ÷ 4.54609
US gallons = Litres ÷ 3.785411784

Worked example

Take 50 litres — a common fuel-fill figure. Divide by 4.54609: 50 ÷ 4.54609 = 11.00 UK gallons. Divide the same 50 litres by 3.785411784 instead: 50 ÷ 3.785411784 = 13.21 US gallons. The identical real-world volume produces two genuinely different numbers depending on which gallon is used — not a rounding difference, a definitional one.

Converting the other way: gallons to litres

To go from gallons back to litres, multiply instead of dividing: UK gallons × 4.54609, or US gallons × 3.785411784. For example, 10 UK gallons = 45.46 litres, while 10 US gallons = 37.85 litres.

Real-world comparisons

• A UK jerry can (20L / 4.4 UK gal): the standard portable fuel container size sold in the UK.
• A typical mid-size car fuel tank (55–60L / 12–13.2 UK gal): a common tank capacity for a UK family hatchback or saloon.
• An oil drum (205L / 45.1 UK gal): the standard industrial drum size, close to the "200 litres" figure frequently searched.
• A watering can (9–10L / 2 UK gal): a typical full-size garden watering can capacity.
• UK vs US car fuel economy figures: because the imperial gallon is larger, a car's mpg figure calculated in UK gallons will always look higher than the same car's mpg calculated in US gallons — roughly 20% higher, purely from the unit difference, not the car's actual efficiency.

Extended small-volume litres to gallons table

For smaller quantities — paint tins, bottles, containers under 10 litres:

And the reverse direction — gallons converted into litres, for both systems:

Historical context: one gallon, two legal definitions

Before 1824, Britain itself used several different gallons — an ale gallon, a wine gallon, and a corn gallon, each a different size, which caused real problems for trade and taxation. The Weights and Measures Act 1824 replaced all of them with a single imperial gallon, legally defined as the volume of 10 pounds of distilled water under specified conditions — a definition later refined in metric terms to exactly 4.54609 litres by the Weights and Measures Act 1985.

The United States, independent since 1776, never adopted Britain's 1824 reform. It kept using the older English wine gallon — defined as 231 cubic inches — which converts to exactly 3.785411784 litres. That single historical fork is the entire reason the UK and US have used two different, incompatible gallons for exactly two centuries, with no sign of either side switching.

The UK itself moved to metric litres as the primary legal unit for fuel and most liquid retail from the 1980s and 90s onward, but the imperial gallon survives in mpg (miles per gallon) figures, some historical vehicle and container specifications, and general conversation about tank sizes and capacities.

Where the UK gallon is still used today

• Fuel economy (mpg): UK-published miles-per-gallon figures use the imperial gallon, which is why they read higher than the equivalent US mpg number for the same real-world efficiency.
• Historical and classic vehicle specifications: older UK car manuals and specification sheets often quote fuel tank capacity and consumption in imperial gallons.
• Agricultural and industrial contexts: some UK farming and industrial equipment capacity figures are still discussed in gallons alongside litres.
• Everyday estimation: "a gallon" remains a rough mental unit some UK speakers still use for larger volumes, even though litres are what's actually printed on the pump or container.

Everyday UK shopping, by contrast, is now almost entirely litre-based: milk cartons are labelled in litres (sometimes alongside pints), bottled water and soft drinks come in litre and half-litre sizes, and household chemicals, paint and fuel additives are sold in millilitre or litre quantities. The gallon has effectively retreated to a small number of specific technical and historical contexts rather than general retail — which is why most UK adults can picture a 2-litre bottle instantly but would struggle to picture a gallon without converting it first.

Common mistakes when converting litres to gallons

• Using the US gallon for a UK fuel or mpg figure. This is the single most common error — it understates a UK car's true fuel-tank capacity or overstates its US-equivalent economy by roughly 20%, since the US gallon is smaller than the imperial gallon.
• Comparing UK and US mpg figures directly. A car quoted at "40mpg" in the UK and "40mpg" in the US are not achieving the same real-world fuel efficiency — the UK figure reflects a larger gallon, so it corresponds to better actual efficiency than the same number would in the US.
• Using a rounded "4.5 litres per gallon" for precise work. The exact UK figure is 4.54609 litres — close enough to 4.5 for a rough mental estimate, but not precise enough for engineering, commercial fuel calculations, or anything where a 1% error compounds across a large volume.
• Assuming "gallon" always means the same thing in older UK sources. Pre-1824 British gallons (ale, wine, corn) differed from the modern imperial gallon — genuinely historical documents may use a different figure, though this is now a rare practical concern outside historical research.

Accuracy and precision note

Both the UK/imperial gallon (4.54609 litres exactly) and the US gallon (3.785411784 litres exactly) are precisely defined legal values, so every conversion here is mathematically exact rather than approximated — the only rounding is in how many decimal places are displayed. For fuel, engineering or commercial calculations where the difference matters, always confirm which gallon a source figure is using before comparing it to a UK litre measurement.

A quick note

All conversions above use the exact legal definitions of the imperial and US gallon. For anything precision-critical (fuel, engineering or commercial use), always confirm against the source figures rather than a rounded display value.

References

• Weights and Measures Act 1985 (legislation.gov.uk)
• GOV.UK: weights, measures and packaging — the law