- 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).
The ounce (abbreviated oz, from the former Italian word onza, now spelled oncia; apothecary symbol: ℥) is a unit of mass with several definitions, the most commonly used of which is equal to approximately 28 grams. The ounce is used in a number of different systems, including those of mass that form part of the United States customary, and imperial, systems. The size of an ounce varies between systems. The most commonly used ounces today are the international avoirdupois ounce and the international troy ounce.
Ounce derives from Latin uncia, a unit that was one twelfth (1/12) of the Roman pound (libra). Ounce was borrowed twice: first into Old English as ynsan or yndsan from an unattested Vulgar Latin form with ts for c before i (palatalization) and second into Middle English through Anglo-Norman and Middle French (unce, once, ounce).
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|
|Maria Theresa ounce||28.0668|
|Dutch metric ounce||100|
|Chinese metric ounce||50|
International avoirdupois ounce 
The avoirdupois ounce is the most commonly used ounce today. It is defined to be one sixteenth of an avoirdupois pound. The avoirdupois pound is defined as 7000 grains; one ounce is therefore equal to 437.5 grains.
In the international yard and pound agreement of 1959 the United States and countries of the Commonwealth of Nations agreed to define the international avoirdupois ounce 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.
International troy ounce 
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,
- a fine ounce is a troy ounce of pure gold content in a gold bar, computed as fineness multiplied by gross weight
- a standard ounce is a troy ounce of 22 carat gold, 91.66% pure (an 11 to 1 proportion of gold to 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)
Apothecaries' ounce 
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.
Spanish ounce 
Metric ounces 
The unit metric ounce is 25 grams and 20 make the metric pound of 500 grams.
Some countries have redefined their ounces in the metric system. For example, the German apothecaries ounce of 30 grams, is very close to the previously widespread Nuremberg ounce, but the divisions and multiples come out in metric.
In 1820, the Dutch redefined their ounce (in Dutch, ons) as 100 grams. Dutch amendments to the metric system, such as an ons or 100 grams, has been inherited, adopted, and taught in Indonesia beginning in elementary school. It is also listed as standard usage in Indonesia's national dictionary, the Kamus Besar Bahasa Indonesia, and the government's official elementary‐school curriculum.
East Asia has a traditional ounce, known as a tael, of varying value. The katti of 16 tael, originally 4⁄3 lb avoirdupois, is now 600 grams. The corresponding tael or tail is then 37.5 grams. 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.
The "ounce" in "ounce-force" is equivalent to an avoirdupois ounce; ounce-force is a measurement of force using avoirdupois ounces. However, it is not necessary to identify it as such or to differentiate it in that way because there is no equivalent measure of force using troy or any other "ounce".
Fluid ounce 
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 about 30 ml in the US system. The fluid ounce is sometimes referred to simply as an "ounce" in applications where its use is implicit. The imperial fluid ounce is also equivalent to the volume occupied by 1 imperial ounce of water weighed in air at 62 °F.
Other uses 
Fabric weight 
Ounces are also used to express the "weight", or more accurately the areal 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.
Notes and references 
- uncia. Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project.
- "ounce". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005.
- "The Units of Measurement Regulations 1995 (Article 4)". 2000-09-20. Retrieved 2009-01-26.
- London Bullion Market Association. "Market Basics".
- Greenfield, Richard (1965). Ethiopia: a new political history. F. A. Praeger. p. 327.
- Ethiopia observer 6. 1962. pp. 187–8.
- Diccionario de la Real Academia Española, 23rd edition, libra
- Diccionario de la Real Academia Española, 23rd edition, onza
- Cardarelli, François (1999). Encyclopaddia of Scientific Units, Weights and Measures. Springer. ISBN 1-85233-682-X.
- Wittop Koning, D. A.; Houben, G. M. M. (1980). 2000 jaar gewichten in de nederlanden. Lochem-Poperinge: De Tijdstroom. ISBN 9060879651. (Dutch)
- "Guide to The Hague – Where to turn". Archived from the original on 2008-03-16. Retrieved 2008-01-01.
- "Nederlands metriek stelsel". Retrieved 2008-01-01.
- "How to shop the fabric market". Retrieved 2008-12-10.
- "How Many? A Dictionary of Units of Measurement". Retrieved 2008-12-10.