A gallon is a unit of volume used to measure liquids, and it is equal to 3.785 liters. The US gallon is defined as 231 cubic inches (3.785 liters), while the imperial gallon, used in the United Kingdom, Canada, and some Caribbean nations, is defined as 4.54609 liters. In both systems, the gallon is divided into four quarts, which are then divided into two pints and pints are divided into two cups.

To convert gallons to liters, you can use the conversion ratio of 1 gallon = 3.785 liters. Alternatively, you can multiply the volume in gallons by 3.785412 to get the volume in liters.

In summary, a gallon is equal to 3.785 liters.