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The ounce (abbreviated oz; apothecary symbol: ) is a unit of mass, weight, or volume used in most British derived customary systems of measurement. The common avoirdupois ounce (approximately 28.3 g) is 116 of a common 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 sometimes also elsewhere in the Anglosphere.

Apothecaries system historical system of mass and volume units that were used by physicians and apothecaries for medical recipes

The apothecaries' system or apothecaries' weights and measures is a historical system of mass and volume units that were used by physicians and apothecaries for medical recipes, and also sometimes by scientists. The English version of the system is closely related to the English troy system of weights, the pound and grain being exactly the same in both. It divides a pound into 12 ounces, an ounce into 8 drachms, and a drachm into 3 scruples or 60 grains. This exact form of the system was used in the United Kingdom; in some of its former colonies it survived well into the 20th century. The apothecaries' system of measures is a similar system of volume units based on the fluid ounce. For a long time, medical recipes were written in Latin, often using special symbols to denote weights and measures.

Mass measure of the resistance of a physical body to acceleration; also determines the strength of its gravitational attraction

Mass is both a property of a physical body and a measure of its resistance to acceleration when a net force is applied. The object's mass also determines the strength of its gravitational attraction to other bodies.

In science and engineering, the weight of an object is related to the amount of force acting on the object, either due to gravity or to a reaction force that holds it in place.


Besides the common ounce, several other ounces are in current use:

Precious metal rare, naturally occurring metallic chemical element of high economic and cultural value

A precious metal is a rare, naturally occurring metallic chemical element of high economic value. Chemically, the precious metals tend to be less reactive than most elements. They are usually ductile and have a high lustre. Historically, precious metals were important as currency but are now regarded mainly as investment and industrial commodities. Gold, silver, platinum, and palladium each have an ISO 4217 currency code.

Force Any interaction that, when unopposed, will change the motion of an object

In physics, a force is any interaction that, when unopposed, will change the motion of an object. A force can cause an object with mass to change its velocity, i.e., to accelerate. Force can also be described intuitively as a push or a pull. A force has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of newtons and represented by the symbol F.

Volume quantity of three-dimensional space

Volume is the quantity of three-dimensional space enclosed by a closed surface, for example, the space that a substance or shape occupies or contains. Volume is often quantified numerically using the SI derived unit, the cubic metre. The volume of a container is generally understood to be the capacity of the container; i. e., the amount of fluid that the container could hold, rather than the amount of space the container itself displaces. Three dimensional mathematical shapes are also assigned volumes. Volumes of some simple shapes, such as regular, straight-edged, and circular shapes can be easily calculated using arithmetic formulas. Volumes of complicated shapes can be calculated with integral calculus if a formula exists for the shape's boundary. One-dimensional figures and two-dimensional shapes are assigned zero volume in the three-dimensional space.

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


Ounce derives from Latin uncia , a unit that was one-twelfth (112) [1] 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). [2] The abbreviation oz came later from the cognate Italian word onza (now spelled oncia).

Latin Indo-European language of the Italic family

Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets, and ultimately from the Phoenician alphabet.

The uncia was a Roman unit of length, weight, and volume. It survived as the Byzantine liquid ounce and the origin of the English inch, ounce, and fluid ounce.

Ancient Roman units of measurement

The ancient Roman units of measurement were largely built on the Hellenic system, which in turn was built upon Egyptian and Mesopotamian influences. The Roman units were comparatively consistent and well documented.

Inch comes from the same Latin word, but differs because it was borrowed into Old English and underwent i-mutation or umlaut ([u]  [y]) and palatalization ([k]  [tʃ]).[ citation needed ]

The inch is a unit of length in the (British) imperial and United States customary systems of measurement. It is equal to ​136 yard or ​112 of a foot. Derived from the Roman uncia ("twelfth"), the word inch is also sometimes used to translate similar units in other measurement systems, usually understood as deriving from the width of the human thumb. Standards for the exact length of an inch have varied in the past, but since the adoption of the international yard during the 1950s and 1960s it has been based on the metric system and defined as exactly 2.54 cm.

The Germanic umlaut is a type of linguistic umlaut in which a back vowel changes to the associated front vowel (fronting) or a front vowel becomes closer to (raising) when the following syllable contains, , or. It took place separately in various Germanic languages starting around AD 450 or 500 and affected all of the early languages except Gothic. An example of the resulting vowel alternation is the English plural foot ~ feet.


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.

Mass of ounce units
International avoirdupois ounce28.349523125437.5
International troy ounce31.1034768480
Apothecaries' ounce
Maria Theresa ounce28.0668 
Spanish ounce (onza)28.75 
French ounce (once)30.59 
Portuguese ounce (onça)28.69 
Roman/Italian ounce (oncia)27.4 
Dutch metric ounce (ons)100 
Dutch (pre-metric) ounce (ons)30 
Chinese metric ounce (盎司)50 
English Tower Ounce29.16450

Currently in use

International avoirdupois ounce

The international avoirdupois ounce is defined as exactly 28.349523125 g under the international yard and pound agreement of 1959, signed by the United States and countries of the Commonwealth of Nations.

The international yard and pound are two units of measurement that were the subject of an agreement among representatives of six nations signed on 1 July 1959, namely the United States, United Kingdom, Canada, Australia, New Zealand and the Union of South Africa. The agreement defined the yard as exactly 0.9144 meters and the pound as exactly 0.45359237 kilograms.

Commonwealth of Nations Intergovernmental organisation

The Commonwealth of Nations, normally known as the Commonwealth, is a sui generis political association of 53 member states, nearly all of them former territories of the British Empire. The chief institutions of the organisation are the Commonwealth Secretariat, which focuses on intergovernmental aspects, and the Commonwealth Foundation, which focuses on non-governmental relations between member states.

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.

Grain (unit) unit of mass

A grain is a unit of measurement of mass, and in the troy weight, avoirdupois, and Apothecaries' system, equal to exactly 64.79891 milligrams. It is nominally based upon the mass of a single virtual ideal seed of a cereal. From the Bronze Age into the Renaissance the average masses of wheat and barley grains were part of the legal definitions of units of mass. Rather, expressions such as "thirty-two grains of wheat, taken from the middle of the ear" appear to have been ritualistic formulas, essentially the premodern equivalent of legal boilerplate. Another source states that it was defined as the weight needed for 252.458 units to balance a cubic inch of distilled water at 30 inches of mercury pressure and 62 degrees Fahrenheit for both the air and water. Another book states that Captain Henry Kater, of the British Standards Commission, arrived at this value experimentally.

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. In addition it is the normal measure for portion sizes in British restaurants. [3]

International troy ounce

A troy ounce 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, 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 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 [4]
  • 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

Some countries have redefined their ounces in the metric system. [5] 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. [6] [7] 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. [8]


Apothecaries' ounce

The obsolete apothecaries' ounce (abbreviated ) equivalent to the troy ounce, was formerly used by apothecaries.

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. [9] [10] 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 ]

Spanish ounce

The Spanish pound (Spanish libra) was 460 g. [11] The Spanish ounce (Spanish onza) was 116 of a pound, i.e. 28.75 g. [12]

Tower ounce

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.[ citation needed ]


An ounce-force is 116 of a pound-force, or 0.2780139 newtons.

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 28.4 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

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. [13] [14]

Fabric typeTypical weight in ounces
Organza, voile, chiffon 1–3
Most cottons, wools, silks, muslin, linen 4–7
Denim, corduroy, twill, velvet 7–16

Copper layer thickness of a printed circuit board

The most common unit of measure for the copper thickness on a printed circuit board (PCB) is ounces (oz). It is the resulting thickness when 1 oz of copper is pressed flat and spread evenly over a one-square-foot area. This roughly equals 34.7 µm. [15]

Notes and references

  1. uncia . Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project .
  2. "ounce". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
  3. "The Units of Measurement Regulations 1995 (Article 4)". 2000-09-20. Retrieved 2009-01-26.
  4. London Bullion Market Association. "Market Basics". Archived from the original on 2012-03-08.
  5. Wittop Koning, D. A.; Houben, G. M. M. (1980). 2000 jaar gewichten in de nederlanden (in Dutch). Lochem-Poperinge: De Tijdstroom. ISBN   9060879651.(in Dutch)
  6. "Guide to The Hague – Where to turn". Archived from the original on 2008-03-16. Retrieved 2008-01-01.
  7. nl:Nederlands metriek stelsel
  8. Ons in KBBI
  9. Greenfield, Richard (1965). Ethiopia: a new political history. F. A. Praeger. p. 327.
  10. Ethiopia observer. 6. 1962. pp. 187–8.
  11. Diccionario de la Real Academia Española, 23rd edition, libra
  12. Diccionario de la Real Academia Española, 23rd edition, onza
  13. "How to shop the fabric market" . Retrieved 2008-12-10.
  14. "How Many? A Dictionary of Units of Measurement" . Retrieved 2008-12-10.
  15. "Copper Thickness FAQ" . Retrieved 2016-11-13.

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Avoirdupois system system of weights (more properly, mass) based on a pound of 16 ounces

The avoirdupois system is a measurement system of weights which uses pounds and ounces as units. It was first commonly used in the 13th century and was updated in 1959.

A pennyweight is a unit of mass that is equal to 24 grains, ​120 of a troy ounce, ​1240 of a troy pound, approximately 0.054857 avoirdupois ounce and exactly 1.55517384 grams.

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A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Systems of measurement in use include the International System of Units (SI), the modern form of the metric system, the imperial system, and United States customary units.

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