This article is about the unit of mass. For the unit of force, see Pound-force. For the unit of volume, see Fluid ounce. For all other uses, see Ounce (disambiguation).

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The ounce (abbreviated: oz, the old Italian word onza, now spelled oncia; apothecary symbol: ℥) is a unit of mass with several definitions, the most commonly used of which are equal to approximately 28 grams. The ounce is used in a number of different systems, including various systems of mass that form part of the imperial and United States customary systems. Its size can vary from system to system. The most commonly used ounces today are the international avoirdupois ounce and the international troy ounce.

Contents 1 Etymology 2 Definitions 2.1 International avoirdupois ounce 2.2 International troy ounce 2.3 Apothecaries' ounce 2.4 Maria Theresa ounce 2.5 Metric ounces 3 Other uses 3.1 Fabric weight 4 Notes and references 5 External links

[edit] Etymology

The origin of the word derives from the Latin uncia, meaning one twelfth (1/12) as the Roman pound (libra) was divided into 12 ounces (unciae).

[edit] Definitions

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). An ounce is more often a measure of force as opposed to mass or weight, comparable to lbf, or pound force. Some of these other ounces are described below.

Summary of ounce units

ounce variant	mass in grams	mass in grains
International avoirdupois ounce	28.3495231	437.5
International troy ounce	31.1034768	480
Apothecaries' ounce
Maria Theresa ounce	28.0668	433.137
Dutch metric ounce	100	1,543.236
Chinese metric ounce	50	771.618
Note: The grain values for the Maria Theresa, Dutch and Chinese ounces are rounded to the nearest thousandth of a grain.

[edit] International avoirdupois ounce

The avoirdupois ounce is the most commonly used ounce today. It is defined to be one sixteenth of an avoirdupois pound. It is therefore equal to 437.5 grains.^{[clarification needed]}

In 1958 the United States and countries of the Commonwealth of Nations agreed to define the international avoirdupois pound to be exactly 0.45359237 kilograms. Consequently, since 1958, the international avoirdupois ounce is exactly ^0.45359237⁄₁₆ kg (28.349523125 g) by definition.

The ounce is commonly used as a unit of mass in the United States. On January 1, 2000, it ceased to be a legal unit of measure within the United Kingdom for economic, health, safety or administrative purposes^[1] but remains a familiar unit, especially amongst older people.

[edit] International troy ounce

A troy ounce (abbreviated as t oz) is equal to 480 grains. Consequently, the international troy ounce is equal to exactly 31.1034768 grams. There are 12 troy ounces in the now obsolete troy pound.

Today, the troy ounce is used only to express the mass of precious metals such as gold, platinum, palladium 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)
• in modern day, an ounce of gold (1 troy ounce) is referred as a 99.99% pure gold piece or gold grains (gold shot)

[edit] Apothecaries' ounce

The obsolete apothecaries' ounce (abbreviated ℥) equivalent to the troy ounce, was formerly used by apothecaries (now called pharmacists or chemists).^{[citation needed]}

[edit] Maria Theresa ounce

"Maria Theresa ounce" was once introduced in Ethiopia and some European countries, which was equal to the weight of one Maria Theresa thaler, or 28.0668 g. Both the weight and the value are the definition of one "Birr", still in use in present-day Ethiopia and formerly in Eritrea.^{[citation needed]}

[edit] Metric ounces

Some countries have redefined their ounces to fit in with the metric system^[2].

The Dutch have redefined their ounce (in Dutch, ons) as 100 grams^[3][4]. The Dutch's metric values, such as 1 ons = 100 grams, is inherited, adopted and taught in Indonesia since elementary school. It is also formally written in Indonesian national dictionary (Kamus Besar Bahasa Indonesia) and elementary school's formal manual book.

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.^{[citation needed]}

[edit] Other uses

[edit] Fabric weight

Ounces are also used to express the "weight", or more accurately density, of a textile fabric in North America, Asia or the UK, as in "16 oz denim". The number refers to the weight in ounces of a given amount of fabric, either a yard of a given width, or a square yard.^[5][6]

[edit] Notes and references

[edit] External links

• Dictionary of Units: Ounce