Ounce

The ounce (abbreviation: oz) is the name of a unit of mass in a number of different systems, including various systems of mass that formed part of English units, Imperial units, and United States customary units. Its size can vary from system to system. The most commonly used ounces used today are the international avoirdupois ounce and the international troy ounce.

The abbreviation "oz" comes from the old Italian word "onza" (now spelled oncia), meaning ounce.

The distinction between mass and weight (or force), and its development, is discussed in the article on weight.

International avoirdupois ounce

Main article: avoirdupois

An avoirdupois ounce is equal to 437.5 grains. There are 16 avoirdupois ounces in an avoirdupois pound. In 1958 the United States and countries of the Commonwealth of Nations defined the mass of the international avoirdupois pound to be 0.453 592 37 kilograms. Consequently, since the definition of the international avoirdupois pound in 1958, the international ounce is defined to be equal to about 28.349 523 grams.

The ounce is commonly used as a unit of mass in the United States. While imperial units have been officially abolished in the United Kingdom, the ounce remains a familiar unit, especially amongst older people.

International troy ounce

Main article: Troy weight

A troy ounce (abbreviation: t oz) is equal to 480 grains. There are 12 troy ounces in a troy pound. Consequently, the international troy ounce is equal to about 31.103 476 grams.

Today, the troy ounce is used only to express the mass of precious metals such as gold, platinum or silver.

For historical measurement of gold,

• a fine ounce is a troy ounce of 99.5% ("995") pure gold
• a standard ounce is a troy ounce of 22 carat gold, 91.66% pure (11 "fine ounces" plus one ounce of alloy material).

Other ounces

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 different standards of mass (or weight, before the distinction between weight and mass developed). Some of these other ounces are described below.

Roman uncia or ounce

Main article: Ancient Roman units of measurement

A Roman uncia (plural: unciae) or ounce is an ancient unit of mass. A different unit of mass was used for monetary purposes than the unit of mass used for commerce. The unit of mass used for commerce was equivalent to approximately 27.3 grams. The name means a twelfth part, and there were 12 unciae in one Roman libra (a unit of mass used for commerce) and 12 unciae in one Roman as (a unit of mass used for monetary purposes).^[1]

Apothecaries' ounce

Main article: Apothecaries' system of mass

An 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 ℥ (U+2125).

Maria Theresa ounce

"Maria Theresa ounce" was once introduced in Ethiopia and some European countries, which was equal to 31.1025 g.^{[citation needed]}

Metric ounces

Main article: kilogram

Some countries have redefined their ounces to fit in with the metric system.

The Dutch have redefined their ounce (in Dutch, ons) as 100 grams. This was adopted along with the introduction of the metric system and remains in informal usage.

East Asia has a traditional ounce, known as a tael, of varying value. In China, it has been given a metric value of 50 grams.

References

1. ^ Sizes, Inc. (2001-10-11). "Roman smaller units of mass". Retrieved on 2006-08-13.

See also

fluid ounce

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