1 U.S. gallon is equal to 3.79 liters, rounded to the nearest hundredth. In the United Kingdom, Imperial gallons are used.1 Imperial gallon is equal to 4.55 liters, rounded to the nearest hundredth.
The liter is not an SI unit, although it is considered an acceptable unit to measure volume. The SI unit for volume is the cubic meter, which is equal to 1000 liters. SI stands for Système International and is the technical measure for scientific measurement. There are base SI units and derived SI units. Base units include the meter, to measure distance, and the kilogram, to measure weight. Derived units include the cubic meter and the square meter to measure area.