The ounce is the name for a number of different units of mass (oz), and, confusingly, fluid volume (fl oz). 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 28.3 grams.
• troy ounce defined by the troy system of mass. In troy weight, unlike the more common avoirdupois system, there are 12 ounces in a pound, rather than 16, and a troy pound is 5760 grains (approx. 373.24 grams), rather than 7000 (approx 453.59 grams). Note: at roughly 31.1 g, the troy ounce is about 10% more than the more common avoirdupois ounce.
• The fluid ounce unit of volume also exists in the two versions of 28.4 (Imperial) and 29.6 ml (U.S.).

The Dutch term ons is a unit of mass that is considerably more, 100 grams.

External links

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