Gallon to Liters - How Many Liters in a Gallon?
Convert US and Imperial gallons to liters for fuel, cooking and daily life
1 US Gallon = 3.785 Liters
One US gallon equals 3.78541 liters - often rounded to 3.8 liters.
Gallons to Liters Conversion Table
| US Gallons | Liters | Common Use |
|---|---|---|
| 0.5 gal | 1.89 L | Half gallon of juice |
| 1 gal | 3.785 L | Milk jug |
| 2 gal | 7.57 L | Large water container |
| 5 gal | 18.93 L | Water cooler bottle |
| 10 gal | 37.85 L | Small aquarium |
| 15 gal | 56.78 L | Beer keg |
| 20 gal | 75.71 L | Medium aquarium |
What is a gallon?
A gallon is the largest common volume unit in the US customary system. Two versions exist: the US gallon and the Imperial (UK) gallon. One US gallon holds exactly 3.785411784 liters. One Imperial gallon holds 4.54609 liters. The British version is about 20% larger than the American one.
The formula is simple: liters = gallons x 3.78541. To reverse: gallons = liters / 3.78541. For quick estimates, round to 3.8 liters per gallon. The error is under 0.4%, which works for most practical purposes.
US gallon vs. Imperial gallon
The US gallon comes from the old English wine gallon, defined as 231 cubic inches. The Imperial gallon was introduced in Britain in 1824 as the volume of 10 pounds of water. That historical difference produces two very different volumes:
- 1 US gallon: 3.785 liters (3,785 ml)
- 1 Imperial gallon: 4.546 liters (4,546 ml)
The gap is about 760 ml per gallon - nearly a full wine bottle. This matters most at the gas pump. Fuel economy figures in miles per gallon (mpg) differ depending on which gallon you use. A car rated at 30 mpg (US) would be about 36 mpg (Imperial). When you compare fuel prices across countries, always check which gallon applies.
A gallon of gas, a road map, and the open highway - that's all you need.
American travel magazine, circa 1955How a gallon breaks down
The US gallon divides neatly into smaller units. Each step doubles the previous one:
- 1 gallon = 4 quarts = 3.785 L
- 1 gallon = 8 pints = 3.785 L
- 1 gallon = 16 cups = 3.785 L
- 1 gallon = 128 fluid ounces = 3.785 L
The Imperial gallon uses different sub-units: 1 Imperial gallon = 4 UK quarts = 8 UK pints = 160 Imperial fluid ounces. A UK pint (568 ml) is larger than a US pint (473 ml). That is why a pint of beer in London holds more than one in New York.
Gallons at the gas station
Fuel prices in the US are listed per US gallon. To convert to price per liter, divide by 3.785. Example: $3.50 per gallon divided by 3.785 equals $0.92 per liter. A typical US car has a tank of 12 to 16 gallons, which is 45 to 60 liters.
Fuel economy in the US is measured in miles per gallon (mpg). Most of the world uses liters per 100 km. To convert: divide 235.21 by the mpg value. So 30 mpg equals 7.84 L/100 km. A hybrid rated at 50 mpg uses about 4.7 L/100 km.
Gallons in daily life
The gallon jug is a staple in American kitchens. Milk, water, juice, and iced tea all come in gallon containers (3.785 liters). The half gallon (1.89 liters) is another common size. Outside the kitchen, you will find gallons on paint cans, cleaning products, and pool chemicals.
Water cooler bottles hold 5 gallons (18.93 liters). Aquarium sizes are measured in gallons: a 10-gallon tank holds 37.85 liters, a 55-gallon tank holds 208 liters. When you buy fish tank equipment rated for a certain gallon capacity, multiply by 3.785 to get liters.
Converting gallons for European use
If you follow American recipes, you rarely need full gallons. Most cooking calls for quarts, cups, or ounces. But some recipes for large batches - like homebrew beer or canning - do use gallons. A 5-gallon homebrew batch produces about 19 liters of beer, which fills roughly 50 standard 375 ml bottles.
For road trips in the US, a quick conversion helps you budget fuel costs. Remember: 1 gallon is just under 4 liters. A 15-gallon tank holds about 57 liters. If you drive 300 miles on a full tank, that is roughly 480 km - similar to what a European compact car covers on 57 liters.
US gallon vs. Imperial gallon - quick comparison
| Property | US Gallon | Imperial Gallon |
|---|---|---|
| Volume in liters | 3.785 L | 4.546 L |
| Volume in ml | 3,785 ml | 4,546 ml |
| Fluid ounces | 128 fl oz | 160 fl oz |
| Pints | 8 US pints | 8 UK pints |
| Used in | USA, some Latin America | UK (historically), Canada (historically) |
Quick rule: 1 gallon is roughly 4 liters. For more accuracy, subtract about 5%: 4 liters minus 0.2 gives you 3.8 liters. Close enough for gas, groceries, and pool chemicals.
Frequently asked questions
How many liters of gas are in a gallon?
One US gallon of gasoline holds 3.785 liters. It weighs about 2.7 kg because gasoline is lighter than water.
Why is the UK gallon bigger?
The Imperial gallon (4.546 L) was defined as the volume of 10 pounds of water in 1824. The US gallon (3.785 L) is based on the older wine gallon of 231 cubic inches.
How do I convert mpg to L/100 km?
Divide 235.21 by the mpg value. Example: 30 mpg = 235.21 / 30 = 7.84 L/100 km.
How many cups are in a gallon?
16 US cups. Each cup holds about 237 ml, so 16 cups equal 3,792 ml - one gallon.