The imperial gallon, unit of volume
The imperial gallon holds exactly 4.54609 liters, that is eight imperial pints. It is the gallon of the United Kingdom, Ireland and much of the Caribbean, and it is not the American gallon.
It was born as water. The Weights and Measures Act of 1824 defined it as the volume of ten pounds of distilled water weighed in air at 62 degrees Fahrenheit under a barometric pressure of thirty inches of mercury, a definition that pins a volume to a mass, a temperature and a pressure at once. The Weights and Measures Act 1985 cut those threads and made it exactly 4.54609 liters. The American gallon never followed: it kept the old English wine gallon of 231 cubic inches, which is why the imperial one is larger by 20.1 per cent.
The imperial gallon in other units
| 1 gal UK | 0.00454609 m³ |
| 1 gal UK | 4.54609 l |
| 1 gal UK | 454.609 cl |
| 1 gal UK | 4,546 ml |
| 1 gal UK | 1.20095 gal |
| 1 gal UK | 9.6076 pt |
| 1 gal UK | 153.722 fl oz |
| 1 gal UK | 160 fl oz UK |
| 1 gal UK | 4.8038 qt |
| 1 gal UK | 4 qt UK |
| 1 gal UK | 8 pt UK |
| 1 gal UK | 19.2152 cup |
| 1 gal UK | 18.1844 cup metric |
| 1 gal UK | 22.7305 cup JP |
| 1 gal UK | 307.443 tbsp |
| 1 gal UK | 303.073 tbsp metric |
| 1 gal UK | 227.305 tbsp AU |
| 1 gal UK | 922.33 tsp |
| 1 gal UK | 909.218 tsp metric |
| 1 gal UK | 45.4609 dl |
| 1 gal UK | 0.028594 bbl |
| 1 gal UK | 2.52014 sho |
| 1 gal UK | 25.2014 go |
Frequently asked questions
How many liters are in an imperial gallon?
4.54609 exactly, against 3.785411784 for the American gallon. Both figures are exact by definition, so the conversion between them carries no measurement error at all.
Why is British fuel economy always a higher number?
Because the gallon is bigger. The same car that does 40 miles per US gallon does 48 per imperial gallon, a difference of 20.1 per cent that comes entirely from the unit and not from the engine.
Does Britain still use the gallon?
Fuel is sold by the liter, but consumption is still quoted in miles per gallon, so the gallon survives as a unit of account rather than of sale. A driver buys liters and judges the result in gallons.