There are 3.79 liters in a U.S. gallon. In the British Imperial system of measurement, which is more prevalent in Canada and the U.K., there are 4.54 liters in a gallon. The imperial gallon is equal to roughly 1.2 U.S. gallons.
In both the U.S. and British Imperial systems of measurement, a gallon is equal to 4 quarts or 8 pints. However, in the U.S. system, a gallon is 128 fluid ounces, while an imperial gallon is 160 fluid ounces.
The word "gallon" is thought to derive from the medieval Latin word "galeta," meaning a pail or a liquid measure. Its first appearance in the English language dates back to the 13th century.