A gallon is a unit of measurement for liquid capacity commonly used in the United States and some other countries. One gallon is equivalent to 128 fluid ounces or about 3.785 liters. It is often used to measure beverages, fuel, and other liquids. In the United States, there are two types of gallons: the US gallon and the imperial gallon. The US gallon is smaller than the imperial gallon, which is used in the United Kingdom and is equal to about 4.546 liters. Understanding gallons is important for cooking, driving, and various industries.