The gallons to liters factor
One US gallon equals 3.78541 liters, so to convert US gallons to liters you multiply by 3.78541. For example, 5 gal × 3.78541 = 18.93 L. This is the US liquid gallon; the imperial (UK) gallon is 4.54609 L. Need the reverse? Use the liters to gallons calculator.
The relationship is exact by definition: the US liquid gallon is defined as 231 cubic inches, which works out at 3.785411784 liters. The site rounds to 3.78541, which is accurate to well under a milliliter on a typical household volume.
The same numbers feed straight into the quarts to cups calculator.
How to use this calculator
Enter a volume in US gallons and the converter instantly shows the equivalent in liters, rounded to two decimals — useful for fuel economy, aquariums, and metric recipes. Just multiply gallons by 3.78541.
Everyday reference points: a 5 gal water-cooler bottle is 18.93 L, a 15 gal car tank is 56.78 L, a 55 gal drum is 208.20 L, and a 100 gal aquarium is 378.54 L. To reverse any of these in your head, divide the liters by roughly 3.8.
Watch out for the dry gallon, a separate US unit of 4.40488 L used for grain and produce; this calculator does not use it. Also note that a US fluid ounce is 29.5735 mL while a UK one is 28.4131 mL, so a 128 fl oz US gallon and a 160 fl oz imperial gallon are two genuinely different volumes rather than a labelling quirk.
Worth having open at the same time: the gallons to pounds calculator.
Gallons to liters reference table
Common conversions:
| US gallons | Liters |
|---|---|
| 1 gal | 3.79 L |
| 2 gal | 7.57 L |
| 5 gal | 18.93 L |
| 10 gal | 37.85 L |
| 20 gal | 75.71 L |
Keep the cups to mL calculator nearby for the rest of the same job.
Frequently asked questions
- How do I convert gallons to liters?
- Multiply US gallons by 3.78541. For example, 5 gal × 3.78541 = 18.93 L.
- How many liters are in 5 gallons?
- 5 US gallons equals about 18.93 liters.
- What is 1 gallon in liters?
- One US gallon equals 3.78541 liters.
- Is this the US or UK gallon?
- It uses the US liquid gallon (3.78541 L). The UK imperial gallon is larger at 4.54609 L.
- Which gallon does a fuel economy figure use?
- US car figures use the US gallon of 3.78541 L, while UK figures use the imperial gallon of 4.54609 L. That makes a UK mpg number look about 20% better than a US one for the same car, so never compare the two directly.