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.
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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).
The word is different from inch because inch came directly from Latin, but ounce came through French.
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.
| ounce variant | equivalent in grams | equivalent 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.
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.
In 1958 the United States and countries of the Commonwealth of Nations agreed to define the international avoirdupois pound to be 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.
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. Bullion coins are the most common products produced and marketed in troy ounces, but precious metal bars also exist in gram and kilogram(kg) sizes. (A kilogram bullion bar contains 32.15074657 troy ounces.)
For historical measurement of gold,
The obsolete apothecaries' ounce (abbreviated ℥) equivalent to the troy ounce, was formerly used by apothecaries (now called pharmacists or chemists).
"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.
Some countries have redefined their ounces in the metric system.[2]
In 1820, 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.
An ounce force is 1/16 of a pound-force, or 0.2780139 newton. It is not necessary to identify it as an avoirdupois ounce; there is no troy ounce-force.
A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl.) is a unit of volume equal to about 28 mL in the imperial system or 30 ml in the US system. The fluid ounce is not comparable to the ounce, which measures mass. However, the fluid ounce is sometimes referred to simply as an "ounce" in applications where its use is implicit.
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]