One cup equals eight ounces. Ounces and cups are just two of the imperial units of volume. In the United States, imperial units are used in most recipes for measuring ingredients.
Other imperial units of volume include teaspoons, tablespoons, pints, quarts and gallons. One cup is also the equivalent of 48 teaspoons or 16 tablespoons. Two cups make 1 pint, and 2 pints equal 1 quart. There are, therefore, 4 cups or 32 ounces in 1 quart. Four quarts make 1 gallon, so 16 cups or 128 ounces equal 1 gallon. In the metric system, the system used in most other industrialized nations, the liter and milliliter are units of volume.