Gallons to Liters

In the US the gallon is the everyday large volume. A gallon jug of milk is 3.79 L, a 5-gallon water-cooler bottle 18.9 L, and a 50-gallon water heater 189 L. Aquariums are sold by gallons too, and since fish-stocking and medication guides from outside the US use liters, keepers convert constantly: a 55-gallon tank holds 208 L before you subtract gravel and decorations.

Paint, pool chemicals and garden sprayers follow suit. A backyard pool of 20,000 gallons is about 75,700 L, or 75.7 cubic meters, which matters when a chlorine dose is written per 10,000 L.

Americans driving abroad or reading foreign news meet fuel priced per liter. Divide a per-gallon price by 3.785 to compare: $3.50 a gallon is $0.92 a liter. In the other direction, a car that does 30 US mpg uses 7.84 L/100 km, found by dividing 235.215 by the mpg figure.

The US gallon is exactly 231 cubic inches. Because the inch is exactly 2.54 cm, that fixes the gallon at 3.785411784 L with no rounding.

The UK, and some older Canadian and Caribbean sources, use the imperial gallon of 4.54609 L. It is about 20% larger than the US gallon, so a British 10-gallon figure is 45.5 L, not 37.9 L. British fuel-economy figures look better for the same reason: 30 imperial mpg is about 25 US mpg, or 9.42 L/100 km.

If the source says gallons without naming which, look at its country of origin. The liters to gallons page goes the other way, and quarts and pints are in the unit converter.