Gallon Calculator - Convert Gallons to Liters, Ounces, Cups and More
Enter any volume in gallons (US liquid, UK imperial, or US dry) and instantly see the equivalent in every other common unit - litres, millilitres, fluid ounces, cups, quarts, pints, cubic inches, cubic feet and more. Switch the gallon type, pick your input unit, and the calculator converts in real time. A water-weight panel shows how much the liquid weighs at cold, room, and hot temperatures.
US gallon vs UK gallon: what is the difference?
The two most common gallon definitions differ by about 20 percent. A US liquid gallon equals exactly 231 cubic inches, which works out to approximately 3.785 litres. A UK (imperial) gallon equals exactly 10 pounds of water at 62 degF, which modern metrology pins at exactly 4.54609 litres. That means one UK gallon is roughly 1.2 US gallons, a difference that matters significantly when comparing fuel economy, beverage sizes, or recipe quantities between the United States and the United Kingdom. The US dry gallon (used mainly for trade measurements of dry goods such as grain or fruit) is a third definition equal to one eighth of a US bushel, or about 4.405 litres - slightly larger than the US liquid gallon but still smaller than the UK gallon.
How to convert gallons to litres
Multiply US liquid gallons by 3.785411784 to get litres. Multiply UK gallons by 4.54609 to get litres. Divide litres by the same factor to go in the other direction. For example, 5 US gallons x 3.785 = 18.93 litres, and 10 litres / 3.785 = 2.642 US gallons. This calculator handles all three gallon types automatically: select the gallon type, choose which unit you are entering, and every other field fills in at once.
Gallons to fluid ounces, cups, quarts and pints
Within the US customary system, 1 US gallon equals exactly 128 US fluid ounces, 16 US cups, 8 US pints, or 4 US quarts. These are exact, defined relationships, so no rounding is needed. In the UK system, 1 UK gallon equals exactly 160 UK fluid ounces, 8 UK pints, or 4 UK quarts - note that a UK pint (568 mL) is larger than a US pint (473 mL). When converting across systems, it helps to go through litres first, which this calculator does internally.
Water weight: how much does a gallon of water weigh?
Water density varies with temperature, so the weight of a gallon of water is not a fixed number. At room temperature (about 25 degC / 77 degF), 1 US liquid gallon of water weighs approximately 3.778 kg or 8.33 lb. At maximum density (about 4 degC / 39 degF), 1 US liquid gallon weighs very close to 3.786 kg or 8.345 lb. Near boiling (100 degC / 212 degF), the density drops to about 0.958 kg/L, so 1 US gallon weighs only about 3.626 kg or 7.99 lb. The water-weight output in this calculator adjusts automatically when you change the temperature selector.
Gallon conversion quick reference
| Unit | US liquid gallon | UK gallon | US dry gallon |
|---|---|---|---|
| Litres | 3.7854 | 4.5461 | 4.4049 |
| Millilitres | 3785.4 | 4546.1 | 4404.9 |
| US fluid ounces | 128 | 153.72 | 148.95 |
| US cups | 16 | 19.215 | 18.618 |
| US quarts | 4 | 4.804 | 4.654 |
| US pints | 8 | 9.608 | 9.309 |
| UK fluid ounces | 133.23 | 160 | 155.04 |
| Cubic inches | 231 | 277.42 | 268.80 |
| Cubic feet | 0.1337 | 0.1605 | 0.1556 |
| Cubic centimetres | 3785.4 | 4546.1 | 4404.9 |
Key equivalents for US liquid, UK imperial and US dry gallons.
Frequently asked questions
How many litres are in a gallon?
It depends on which gallon you mean. A US liquid gallon equals 3.785411784 litres (exact). A UK imperial gallon equals 4.54609 litres (exact). A US dry gallon equals approximately 4.405 litres. The US gallon is the one most commonly meant in everyday American usage.
How many fluid ounces are in a gallon?
A US liquid gallon contains exactly 128 US fluid ounces. A UK imperial gallon contains exactly 160 UK fluid ounces. Note that a US fluid ounce (29.57 mL) and a UK fluid ounce (28.41 mL) are slightly different, so mixing systems will give wrong answers.
How many cups are in a gallon?
A US gallon equals exactly 16 US cups. Because a US cup is defined as exactly 8 US fluid ounces, and there are 128 US fluid ounces in a gallon, the relationship is fixed at 16. This is a useful cooking conversion: a half-gallon is 8 cups, a quart is 4 cups, and a pint is 2 cups.
How much does a gallon of water weigh?
At room temperature (about 25 degC / 77 degF), 1 US gallon of water weighs approximately 3.778 kg or 8.33 lb. A UK gallon at the same temperature weighs about 4.535 kg or 10.0 lb. The exact weight depends on water temperature because warmer water is less dense.
How do I convert cubic feet to gallons?
Multiply cubic feet by 7.48052 to get US gallons, or by 6.22884 to get UK gallons. For example, a tank with a volume of 10 cubic feet holds about 74.8 US gallons or 62.3 UK gallons. This calculator supports cubic feet as an input unit so you can convert directly.
What is the difference between a dry gallon and a liquid gallon?
A US liquid gallon (231 cubic inches, 3.785 L) is used for liquids such as water, fuel, and milk. A US dry gallon (268.8 cubic inches, 4.405 L) is a larger unit used historically for measuring dry commodities such as grain. Dry gallons are rare in modern daily use but still appear in some agricultural and trade contexts in the United States.