Gallons to Liters Calculator

Background.

There are two gallons in everyday use, and they differ by about a fifth. The US liquid gallon is exactly 3.785411784 liters; the imperial gallon used in the United Kingdom is exactly 4.54609 liters, so one imperial gallon holds about 1.2009 US gallons. A label that just says 'gallons' means the US unit on anything sold in the United States and usually the imperial unit on older British equipment, recipes and documents.

Both figures are exact because both gallons are now defined in terms of metric units. The US gallon has always been 231 cubic inches, and since the inch was fixed at exactly 2.54 cm in 1959, 231 × 2.54³ comes to 3,785.411784 cubic centimeters, the factor NIST Special Publication 811 lists. The imperial gallon, first defined as the volume of ten pounds of water, is now set directly at 4.54609 liters by Schedule 1 of the UK's Weights and Measures Act 1985.

Enter a volume, choose which gallon it is in, and the result appears in liters, with the conversion under the other gallon shown alongside in case the source was ambiguous. Where the two answers differ enough to matter, find out which gallon was meant before you size a pump or dose a tank.

What is gallons to liters calculator?

Converting gallons to liters means expressing the same volume in the metric unit, where one liter is one cubic decimeter, or 1,000 cubic centimeters. Both gallons divide into 4 quarts or 8 pints, but the pieces differ: a US gallon holds 128 US fluid ounces of about 29.57 mL each, while an imperial gallon holds 160 imperial fluid ounces of about 28.41 mL.

How to use this calculator.

1. 01Enter the volume in gallons, such as a tank, drum or pool capacity.
2. 02Choose US gallon for anything labelled for the American market, and imperial gallon for UK sources or older British, Irish or Commonwealth documents.
3. 03Read the converted volume in liters; the two lines beneath give the result under each gallon definition.
4. 04If the two lines differ by more than your measurement could tolerate and you are unsure which gallon the source used, check the manufacturer's metric figure before relying on either.

The formula.

Litres = gallons × f, where f is 3.785411784 for the US gallon and 4.54609 for the imperial gallon. Volume conversions have no offset, so zero gallons is zero liters and doubling the gallons doubles the liters. Both factors are exact by definition, so the only uncertainty in the answer is the uncertainty in the gallon figure you start with. The US gallon here is the liquid gallon; the rarely used US dry gallon, about 4.4049 L, is a different unit and is not offered.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Institute of Standards and Technology. NIST Special Publication 811, 2008 Edition - Guide for the Use of the International System of Units (SI), Appendix B. Source for the exact US gallon = 3.785411784 L conversion factor.
2. [2]United Kingdom. Weights and Measures Act 1985, Schedule 1. Statutory definition of the imperial gallon as exactly 4.54609 liters.