One US gallon, in every unit that matters
The US gallon splits cleanly into quarts, pints, cups and fluid ounces by simple whole numbers. Only the metric side needs a real factor.
To go the other way, gallons = liters ÷ 3.78541. Remember the "4-8-16" chain (quarts, pints, cups) and you can do most kitchen conversions in your head.
US and UK gallons are not the same size
This is the one trap. A UK Imperial gallon is about 20% larger than a US gallon, so fuel economy and pricing never compare directly between the two.
One Imperial gallon equals about 1.20 US gallons. A UK driver filling up in America gets roughly 20% less fuel per "gallon" than they would at home.
Quick reference — US gallons
| US Gallons | Liters | Quarts | Cups | Fluid Ounces |
|---|---|---|---|---|
| 1 | 3.79 | 4 | 16 | 128 |
| 2 | 7.57 | 8 | 32 | 256 |
| 5 | 18.93 | 20 | 80 | 640 |
| 10 | 37.85 | 40 | 160 | 1,280 |
There is also a US dry gallon (4.405 L) for grains and produce — separate from the liquid gallon and rarely used today.
Common questions
How many liters are in a gallon?
A US gallon is 3.78541 liters. A UK (Imperial) gallon is larger at 4.54609 liters, about 20% more. Always say which gallon you mean.
Why is the UK gallon bigger than the US gallon?
They come from different standards. The US kept the old English wine gallon of 231 cubic inches, while Britain redefined its Imperial gallon in 1824 as the volume of 10 pounds of water. The Imperial gallon ended up about 20% larger.
How many fluid ounces are in a gallon?
128 US fluid ounces in a US gallon. That breaks down as 4 quarts, 8 pints, or 16 cups. A UK gallon holds 160 UK fluid ounces, since both the gallon and the ounce differ from the US ones.
