Ounce

The ounce (/ˈaʊns/) is any of several different units of mass, weight, or volume and is derived almost unchanged from the uncia, an Ancient Roman unit of measurement.

The avoirdupois ounce (exactly 28.349523125 g) is 1⁄16 avoirdupois pound; this is the United States customary and British imperial ounce. It is primarily used in the United States.

Although the avoirdupois ounce is the mass measure used for most purposes, the 'troy ounce' of exactly 31.1034768 g is used instead for the mass of precious metals such as gold, silver, platinum, palladium, rhodium, etc.

The term 'ounce' is also used in other contexts:

Historically, a variety of different ounces measuring mass or volume were used in different jurisdictions by different trades and at different times in history.

Ounce derives from the Ancient Roman uncia (meaning: a twelfth), a unit in the Ancient Roman units of measurement weighing about 27.4 grams or 96.7% of an avoirdupois ounce, that was one-twelfth (1⁄12) of the Roman pound (libra). This in turn comes from Latin unus ('one'), and thus originally meant simply 'unit'. The term uncia was borrowed twice: first into Pre–Old English, becoming ynce in Old English, which survives in modern English as inch; and a second time into Middle English through Anglo-Norman and Middle French (unce, once, ounce), yielding English ounce. The abbreviation oz came later from the Italian cognate onza, pronounced [ˈontsa] (or later oncia, pronounced [ˈontʃa]).

Historically, in different parts of the world, at different points in time, and for different applications, the ounce (or its translation) has referred to broadly similar but still slightly different standards of mass.

The international avoirdupois ounce (abbreviated oz) is defined as exactly 28.349523125 g under the international yard and pound agreement of 1959, signed by the United States and countries of the Commonwealth of Nations.