A unit of mass in the avoirdupois system of units or volume in the U.S. or British Imperial systems of liquid measure (in the latter case, the ounce is more properly known as the fluidounce). As a mass, the ounce is equal to 1/16 of a pound-mass, or 16 drams. A slightly different ounce known as the Troy ounce is defined in the Troy system of units.

The fluidounce is equal to 1/16 of a pint (which is 1/16 of a pound-volume). Half an ounce is called a tablespoon.

Avoirdupois System of Units, Cup, Dram, Fluidounce, Pound-Mass, Pound-Volume, Troy Ounce