How this calculator works
A gallon is a volume of liquid. The US gallon is exactly 231 cubic inches, or 3.785411784 litres. The imperial gallon, used historically in the United Kingdom and Canada, is exactly 4.54609 litres, so it is about 20 per cent larger. The page converts either gallon to litres, cubic feet, cubic metres, US cups and the other gallon. In water-weight mode it multiplies the volume by the density of water, about 1 kilogram per litre, to give the mass of that volume of water.
Formula
cubic metres = gallons x 0.003785411784 for US gallons, or x 0.00454609 for imperial gallons. Litres = cubic metres x 1,000. Cubic feet = cubic metres / 0.028316846592. US cups = cubic metres / 0.0002365882365. Water mass in kilograms = cubic metres x 1,000, and pounds = kilograms / 0.45359237.
Worked example
1 US gallon is 3.78541 L, 0.832674 imperial gallons, 0.133681 ft3 and 16 US cups. 1 imperial gallon is 4.54609 L and 1.20095 US gallons. One US gallon of water has a mass of 3.78541 kg or 8.3454 lb at about 4 degrees Celsius.
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Frequently asked questions
Is a US gallon the same as an imperial gallon?
No. The US gallon is 3.785411784 L and the imperial gallon is 4.54609 L. The imperial gallon is about 20 per cent larger, so a UK gallon of fuel is more fuel than a US gallon.
How much does a gallon of water weigh?
About 3.785 kg or 8.345 lb for a US gallon at 4 degrees Celsius, and about 4.546 kg or 10.022 lb for an imperial gallon. Water density changes slightly with temperature, so the mass is a little lower when the water is hot.
Why are there 16 cups in a US gallon?
A US cup is defined as 8 US fluid ounces and a US gallon is 128 US fluid ounces, so 128 / 8 = 16 cups. An imperial gallon does not divide into US cups evenly because the gallon systems differ.
What is a dry gallon?
Some agricultural measures use a dry gallon of about 4.4049 L. This page uses liquid gallons only, so dry gallons are not supported.