Litres to Gallons: US vs UK Conversion (3.785L vs 4.546L)

Pick up a hire car in London, fill the tank at a motorway services, and head to a fuel display that’s different from what you’d see in Chicago or Toronto — and suddenly those familiar numbers don’t add up the way they should. The UK and US measurement systems both use “gallons,” but they’re not the same size. Understanding which gallon you’re working with matters whether you’re crossing the Atlantic or just comparing overseas vehicle specifications.

1 US gallon: 3.785 litres · 1 UK gallon: 4.546 litres · 1 litre: 0.264 US gallons · 1 litre: 0.22 UK gallons · 4 litres: 1.057 US gallons

Conversion factors from authoritative reference sources, used for cross-checking all calculations throughout this guide.

How many litres are in a gallon UK?

The UK imperial gallon is defined as exactly 4.54609 litres (Wikipedia — Gallon). This measurement traces its formal roots to the British Weights and Measures Act of 1824, when the imperial system was standardised across the United Kingdom and its territories.

UK imperial gallon definition

The imperial gallon contains 160 fluid ounces, compared to the US system’s 128 fluid ounces per gallon (The Calculator Site). This difference reflects divergent historical development: the imperial system was standardised nearly 50 years after American independence, by which time the US had already locked in its own customary definitions.

Conversion formula

To convert litres to UK gallons: divide the litre value by 4.54609 (or multiply by 0.2199692483). For example, 5 UK gallons equals 22.73 litres (The Calculator Site), and 20 litres equals approximately 4.399 UK gallons.

The pattern: litres ÷ 4.54609 = UK gallons

Is there a difference between a US gallon and a UK gallon?

The UK gallon is approximately 20% larger than the US gallon (Kisskind). This distinction matters enormously when converting volumes for fuel, recipes, industrial applications, or cross-border commerce.

US liquid gallon

The US liquid gallon is defined as 231 cubic inches, equivalent to exactly 3.785411784 litres (Wikipedia — Gallon). It contains 128 fluid ounces. The US gallon is used throughout the United States and in several Latin American and Caribbean countries.

UK imperial gallon

The UK imperial gallon equals 4.54609 litres with 160 fluid ounces per gallon (The Calculator Site). This system is used in the United Kingdom, Ireland, Canada, Australia, New Zealand, India, South Africa, Malaysia, and some Caribbean nations.

Comparison table

Five key differences in measurement systems, summarised for quick reference.

How many litres to 1 gallon?

The answer depends entirely on which gallon you’re measuring. One US gallon equals 3.785411784 litres, while one UK imperial gallon equals 4.54609 litres.

US gallon

To convert US gallons to litres: multiply the gallon value by 3.785411784. To convert litres to US gallons: divide by 3.785411784 (or multiply by 0.2641720524) (The Calculator Site).

UK gallon

To convert UK gallons to litres: multiply by 4.54609. To convert litres to UK gallons: divide by 4.54609 (or multiply by 0.2199692483) (Unit Converters).

Is 4 litres equal to 1 gallon?

No — 4 litres does not equal exactly 1 gallon in either system, though it’s close in the US case.

4 litres in US gallons

Four litres equals approximately 1.0567 US gallons (4 ÷ 3.785411784 = 1.0567) (Unit Converters). This is just over 1 US gallon, so rounding up is common in casual contexts.

4 litres in UK gallons

Four litres equals approximately 0.8799 UK gallons (4 ÷ 4.54609 = 0.8799). This is notably less than 1 UK gallon — the difference of 0.12 UK gallons represents a shortfall of roughly 0.55 litres.

The implication: UK drivers treating 4 litres as “about a gallon” will consistently underfill by over half a litre — a costly habit at the pump.

How to convert liters to gallons step by step?

Follow these steps for accurate conversion, whether you’re working with US or UK measurements.

Formula for US

1. Identify the volume in litres you want to convert
2. Divide by 3.785411784 (the exact US gallon value)
3. Round to your desired precision (3 decimal places for most practical uses)

Example: Convert 10 litres to US gallons. 10 ÷ 3.785411784 = 2.6417 US gallons.

Formula for UK

1. Identify the volume in litres you want to convert
2. Divide by 4.54609 (the exact UK imperial gallon value)
3. Round to your desired precision

Example: Convert 10 litres to UK gallons. 10 ÷ 4.54609 = 2.1997 UK gallons.

Examples: 5L, 10L

Working with 5 litres: this equals 1.321 US gallons or 1.0999 UK gallons. For 15 litres, you’re looking at approximately 3.96 US gallons or 3.30 UK gallons (The Calculator Site). At 100 litres, the conversions reach 26.42 US gallons or 21.997 UK gallons (Unit Converters).

The pattern: litres ÷ 3.785411784 = US gallons; litres ÷ 4.54609 = UK gallons.