Ounce - Definition and Overview

This article is about the unit of measure. Ounce is also another name for the snow leopard.

The ounce is the name for a number of different units of mass (oz), and, confusingly, of two units of fluid volume (fl oz) and of one unit of force, the ounce-force (ozf). See Imperial system of units and U.S. customary units for more about the frameworks within which these units are defined.

• avoirdupois ounce defined by the avoirdupois system of mass (see pound). There are 16 ounces in the avoirdupois pound. The avoirdupois ounce is approximately 28.35 grams.
• troy ounce defined by the troy system of mass. In troy weight, there are 12 ounces in a pound, and a troy pound is 5760 grains (about 373.24 g), rather than 7000 (about 453.59 g). Note: at roughly 31.10 g, the troy ounce is about 10 per cent more than the more-common avoirdupois ounce. These troy ounces are now used only when weighing precious metals like gold and silver. One ounce of gold is always 31.1 g.
• apothecaries' ounce defined by the now-obsolete apothecaries' system of mass. This ounce was the same size as the troy ounce, and its symbol was ℥.

• The fluid ounce unit of volume also exists in the two versions of 28.41 ml (Imperial) and 29.57 ml (U.S.).

• The ounce-force (see pound-force) is the force exerted by a mass of 1 oz avoirdupois at the standard acceleration of gravity, usually borrowing the value which is official for defining kilograms-force, 9.80665 m/s². Thus 1 ozf is approximately 278.0 millinewtons.

The Dutch term ons is a unit of mass that is considerably more, 100 g, a redefinition adopted with the introduction of the metric system together with a redefinition of the Dutch pond as 1 kg. (Though the ons of 100 g remains in informal usage, this pond as a kilogram has fallen by the wayside, replaced by the metric pound of 500 g adopted in other countries.)

Relevant articles

• Weights and measures

External links

• http://www.unc.edu/~rowlett/units/dictO.html#ounce
• http://www.unc.edu/~rowlett/units/dictF.html#fluid_ounce