This article is about the unit of mass. For the unit of volume, see Fluid ounce. For all other uses, see Ounce (disambiguation). An ounce (abbreviated oz; apothecary symbol: ℥) is usually the international avoirdupois ounce as used in the United States customary and British imperial systems, which is equal to one-sixteenth of a pound or approximately 28 grams; however, other definitions of ounce (most importantly, the international troy ounce) are used in a number of different measurement systems. The abbreviation “oz” derives from the Italian word (now spelled ).