What is a UK Gallon?

The UK imperial gallon equals exactly 4.54609 liters and is approximately 20% larger than the US gallon. Established by the British Weights and Measures Act of 1824 to standardize earlier ale and corn gallons, the imperial gallon was designed so that 10 pounds of pure water at 62°F occupied exactly 1 gallon. Although the United Kingdom has officially adopted the liter for fuel sales since 1995, the imperial gallon persists in everyday speech ('miles per gallon' for car fuel economy) and remains the standard unit in some Caribbean and Pacific Commonwealth countries. The imperial gallon relates to the US gallon (1 imp gal ≈ 1.201 US gal), the imperial quart (4 imp qt = 1 imp gal), the imperial pint (8 imp pt = 1 imp gal — the famous British pint of beer), and the liter (1 imp gal ≈ 4.546 L).

Visual reference for how the uk gallon relates to other volume units. Each row links to the full converter for that pair.

See all 15 volume units in matrix view →

• UK fuel economy in miles per gallon (UK mpg)
• Older British industrial and brewing contexts
• Commonwealth countries that retain imperial measures

• ✓1 UK gallon = 4.54609 L exactly = 160 UK fluid ounces.
• ✓1 UK gallon ≈ 1.201 US gallons.
• ✓UK mpg × 0.832 = US mpg (same car, different unit).

• ✗Comparing UK mpg with US mpg directly — UK figures are about 20% higher for the same car.
• ✗Using 4.5 L instead of 4.546 L for precise conversion.
• ✗Assuming modern UK car ads quote US gallons — they always use UK gallons.