How to convert gallons to liters
To convert gallons to liters, multiply each value by the exact factor in the box: 1 US gallon = 3.785411784 liters exactly. There is no rounding anywhere in the chain — the display trims the final answer to six decimal places, and converting the result back with the inverse page returns your starting number.
The gallon on this page is the US gallon: 231 cubic inches, exactly 3.785411784 liters by definition, divided into 4 quarts, 8 pints or 128 fluid ounces. The Imperial gallon of the old British system is a different and larger unit — exactly 4.54609 liters — and this converter does not use it. If your gallon came from an American pump, paint can, milk jug or fish tank, it is the US gallon and the factor above is exact; if it came from a pre-metric British source, convert with 4.54609 instead, or the answer will be 17% light.
Fuel economy is where the conversion turns consequential: a 15-gallon tank is 56.78 L, and an American car's range figure in miles per US gallon becomes the rest of the world's liters per 100 km only through this factor (30 mpg US is 7.84 L/100 km — while 30 mpg in Imperial gallons is 9.4 L/100 km, a difference that has misled many an imported-car buyer). Paint (a gallon covers roughly 350 square feet, in 3.785 L tins abroad), pool chemicals and aquarium volumes — a “55-gallon” tank is 208.2 L — all convert the same way.
The common mistake, beyond the Imperial mix-up, is multiplying by 3.8 or 4 and calling it done: at 50 gallons the ×4 shortcut claims 200 L against the true 189.27 L, an error of nearly three gallons of fuel or paint. Fluid ounces cause the other quiet error — a gallon is 128 US fluid ounces by volume, and converting a recipe's ounces as if they were weight ounces of water works only for water-like liquids. State the factor, state the gallon, and the conversion is unarguable.
Worked example
5 US gallons is 18.927059 liters: 5 × 3.785411784 = 18.927059 — a portable fuel can, stated in US gallons so there is no Imperial ambiguity about the answer.
How to use this converter
- Enter your value in gallons in the box above — the result updates as you type.
- Read the converted value in liters in the headline panel.
- Check the factor, the formula and the inverse result (your answer converted back) in the stats if you need to show your working.
- Use the Gallons to Liters conversion table below for other common values without typing each one.