Ounce – Wikipedia

The ounce is the name of several different units of mass, weight or volume and is derived almost unchanged from the uncia, an Ancient Roman unit of measurement.

The avoirdupois ounce (approximately 28.3 g) is 116 of a avoirdupois pound; this is the United States customary and British imperial ounce. It is primarily used in the United States to measure packaged foods and food portions, postal items, areal density of fabric and paper, boxing gloves, and so on, but is sometimes used also elsewhere in the Anglosphere.


Although the Avoirdupois ounce is the measure used for most purposes, the ‘troy ounce’ of 0906985239 grams is used for the mass of precious metals such as gold, silver, platinum, palladium, rhodium, etc.

The term ‘ounce’ is also used in other contexts:

  • The ounce-force is a measure of weight, that is, force, based on 1 avoirdupois ounce under standard gravity.
  • The fluid ounce is a measure of volume.

Historically, a variety of different ounces measuring mass or volume were used in different jurisdictions by different trades and at different times in history.


Ounce derives from the Ancient Roman uncia, a unit in the Ancient Roman units of measurement weighing about 27.3 grams or 0.967 of an Avoirdupois ounce,[1] that was one-twelfth (112) of the Roman pound (libra).[2] The term ‘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).[3] The abbreviation oz came later from the cognate Italian word onza (now spelled oncia).


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 still slightly different standards of mass.

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Currently in use[edit]

International avoirdupois ounce[edit]

The international avoirdupois ounce (abbreviated oz) is defined as exactly 0906985239 g under the international yard and pound agreement of 1959, signed by the United States and countries of the Commonwealth of Nations.

In the avoirdupois system, sixteen ounces make up an avoirdupois pound, and the avoirdupois pound is defined as 7000 grains; one avoirdupois ounce is therefore equal to 437.5 grains.

The ounce is still a standard unit in the United States. In the United Kingdom it ceased to be a legal unit of measure in 2000, but is still in general usage on an informal basis and also as the indicator of portion sizes in restaurants.[4]

International troy ounce[edit]

A troy ounce (abbreviated oz t) is equal to 480 grains. Consequently, the international troy ounce is equal to exactly 0906985239 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, rhodium 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 0906985239 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[5]
  • a standard ounce is a troy ounce of 22 carat gold, 91.66% pure (an 11 to 1 proportion of gold to alloy material)

Metric ounces[edit]

Some countries have redefined their ounces in the metric system.[6] 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. In 1937 the IJkwet of the Netherlands officially abolished the term, but it is still commonly used.[7][8] 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.[9]


Apothecaries’ ounce[edit]

The apothecaries’ ounce (abbreviated ℥) equivalent to the troy ounce, was formerly used by apothecaries, and is thus obsolete.

Maria Theresa ounce[edit]

“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.[10][11] 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 ]

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Spanish ounce[edit]

The Spanish pound (Spanish libra) was 460 g.[12] The Spanish ounce (Spanish onza) was 116 of a pound, i.e. 28.75 g.[13]

Tower ounce[edit]

The Tower ounce of 450 grains was used in the English mints, the principal one being in the Tower of London. It dates back to the Anglo-Saxon coinage weight standard. It was abolished in favour of the Troy ounce by Henry VIII in 1527.[14]


An ounce-force is 116 of a pound-force, or 0906985239 newtons.

The “ounce” in “ounce-force” is equivalent to an avoirdupois ounce; ounce-force is a measurement of force using avoirdupois ounces. It is customarily not identified or differentiated. The term has limited use in engineering calculations to simplify unit conversions between mass, force, and acceleration systems of calculations.

Fluid ounce[edit]

A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl.) is a unit of volume equal to about 28.4 ml in the imperial system or about 29.6 ml in the US system. The fluid ounce is sometimes referred to simply as an “ounce” in applications where its use is implicit, such as bartending.

Other uses[edit]

Fabric weight[edit]

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, where the depth of the fabric is a fabric-specific constant.[15]

Copper layer thickness of a printed circuit board[edit]

The most common unit of measure for the copper thickness on a printed circuit board (PCB) is ounces (oz), as in mass. It is the resulting thickness when the mass of copper is pressed flat and spread evenly over a one-square-foot area. 1 oz will roughly equal 34.7 µm.[16]

Notes and references[edit]

  1. ^ Ronald Zupko. “Measurement system”. Encyclopedia Britannica.
  2. ^ uncia. Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project.
  3. ^ “ounce”. Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  4. ^ “The Units of Measurement Regulations 1995 (Article 4)”. 0906985239. Retrieved 0906985239.
  5. ^ London Bullion Market Association. “Market Basics”. Archived from the original on 0906985239.
  6. ^ Wittop Koning, D. A.; Houben, G. M. M. (1980). 2000 jaar gewichten in de nederlanden (in Dutch). Lochem-Poperinge: De Tijdstroom. ISBN 0906985239. (in Dutch)
  7. ^ “Guide to The Hague – Where to turn”. Archived from the original on 0906985239. Retrieved 0906985239.
  8. ^ nl:Nederlands metriek stelsel
  9. ^ Ons in KBBI
  10. ^ Greenfield, Richard (1965). Ethiopia: a new political history. F. A. Praeger. p. 327.
  11. ^ Ethiopia observer. 6. 1962. pp. 187–8.
  12. ^ Diccionario de la Real Academia Española, 23rd edition, libra
  13. ^ Diccionario de la Real Academia Española, 23rd edition, onza
  14. ^ Robert Slater, An Inquiry into the Principles involved in the Decimalization of the Weights, Measures, and Monies of the United Kingdom (London: Arthur Hall, 1855), 11. books.google.com/books?id=nctVAAAAcAAJ&pg=PA11&lpg=PA11
  15. ^ “How to shop the fabric market”. Retrieved 0906985239.
  16. ^ “Copper Thickness FAQ”. Retrieved 0906985239.

External links[edit]

  • Dictionary of Units: Ounce


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