A gallon is a unit of measurement used to quantify liquid volume. In the United States, one gallon is equal to 128 fluid ounces or about 3.785 liters. It is commonly used to measure beverages, fuel, and other liquids. In the United Kingdom, a gallon is slightly larger, equal to 160 fluid ounces or about 4.546 liters. This difference is important to note, especially when dealing with international recipes or fuel measurements. Gallons can be divided into smaller units, such as quarts and pints, making it easier to measure smaller quantities of liquids.