The ounce () is any of several different units of

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different eleme ...

weight In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar qua ...

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...

and is derived almost unchanged from the , an Ancient Roman unit of measurement. The avoirdupois ounce (exactly ) is

avoirdupois pound The pound or pound-mass is a unit of mass used in British imperial and United States customary systems of measurement. Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defin ...

; 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 it is sometimes also used elsewhere in the Anglosphere. Although the avoirdupois ounce is the mass measure used for most purposes, the '

troy ounce Troy weight is a system of units of mass that originated in 15th-century England, and is primarily used in the precious metals industry. The troy weight units are the grain, the pennyweight (24 grains), the troy ounce (20 pennyweights), and th ...

' of exactly is used instead 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 force (see below). * The

fluid ounce A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl., old forms ℥, fl ℥, f℥, ƒ ℥) is a unit of volume (also called ''capacity'') typically used for measuring liquids. The British Imperial, the United States customary, and the United ...

is a measure of

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

Etymology

''Ounce'' derives from the Ancient Roman , a unit in the

Ancient Roman units of measurement The ancient Roman units of measurement were primarily founded on the Hellenic system, which in turn was influenced by the Egyptian system and the Mesopotamian system. The Roman units were comparatively consistent and well documented. Length T ...

weighing about 27.35 grams or 0.967 of an Avoirdupois ounce, that was one-twelfth () of the

Roman pound The ancient Roman units of measurement were primarily founded on the Hellenic system, which in turn was influenced by the Egyptian system and the Mesopotamian system. The Roman units were comparatively consistent and well documented. Length T ...

(). This in turn comes from Latin ('one'), and thus originally meant simply 'unit'. The term ''uncia'' was borrowed twice: first into

Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th c ...

as or from an unattested

Vulgar Latin Vulgar Latin, also known as Popular or Colloquial Latin, is the range of non-formal registers of Latin spoken from the Late Roman Republic onward. Through time, Vulgar Latin would evolve into numerous Romance languages. Its literary counterpa ...

form with ''ts'' for ''c'' before ''i'' ( palatalization), which survives in modern English as '' inch'', and a second time into

Middle English Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old English ...

through Anglo-Norman and

Middle French Middle French (french: moyen français) is a historical division of the French language that covers the period from the 14th to the 16th century. It is a period of transition during which: * the French language became clearly distinguished from ...

(), yielding English ''ounce''. The abbreviation ''oz'' came later from the Italian cognate , pronounced (now , pronounced ).

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 still slightly different standards of mass.

Currently in use

International avoirdupois ounce

The international avoirdupois ounce (abbreviated oz) is defined as exactly 28.349523125 g under the

international yard and pound 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: the United States, United Kingdom, Canada, Australia, New Zealand, and South Africa. T ...

agreement of 1959, signed by the United States and countries of the

Commonwealth of Nations The Commonwealth of Nations, simply referred to as the Commonwealth, is a political association of 56 member states, the vast majority of which are former territories of the British Empire. The chief institutions of the organisation are the ...

. In the avoirdupois system, sixteen ounces make up an

, and the avoirdupois pound is defined as 7000

grains A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legumes ...

; 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 The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

it ceased to be an independent unit of measure in 2000, but may still be seen as an (imprecise) indicator of portion sizes in burger and steak restaurants.

International troy ounce

(abbreviated oz t) is equal to 480

. Consequently, the international troy ounce is equal to exactly 31.1034768 grams. There are 12 troy ounces in the now obsolete

troy pound Troy weight is a system of units of mass that originated in 15th-century England, and is primarily used in the precious metals industry. The troy weight units are the grain, the pennyweight (24 grains), the troy ounce (20 pennyweights), and th ...

. Today, the troy ounce is used only to express the mass of precious metals such as

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...

palladium Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...

rhodium Rhodium is a chemical element with the symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring i ...

silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...

Bullion coin Bullion is non-ferrous metal that has been refined to a high standard of elemental purity. The term is ordinarily applied to bulk metal used in the production of coins and especially to precious metals such as gold and silver. It comes fro ...

s 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 .) For historical measurement of gold, * a fine ounce is a troy ounce of pure gold content in a gold bar, computed as

fineness The fineness of a precious metal object (coin, bar, jewelry, etc.) represents the weight of ''fine metal'' therein, in proportion to the total weight which includes alloying base metals and any impurities. Alloy metals are added to increase hardne ...

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 An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...

material)

Metric ounces

Some countries have redefined their ounces in the

metric system The metric system is a system of measurement that succeeded the decimalised system based on the metre that had been introduced in France in the 1790s. The historical development of these systems culminated in the definition of the Interna ...

. 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 Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () Dutch may also refer to: Places * Dutch, West Virginia, a community in the United States * Pennsylvania Dutch Country People E ...

, ''ons'') as 100

gram The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...

s. In 1937 the IJkwet of the Netherlands officially abolished the term, but it is still commonly used. Dutch amendments to the metric system, such as an ''ons'' or 100 grams, has been inherited, adopted, and taught in

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

beginning in elementary school. It is also listed as standard usage in Indonesia's national dictionary, the ''

Kamus Besar Bahasa Indonesia The (''KBBI'' ; ) is the official dictionary of the Indonesian language compiled by Language Development and Fostering Agency and published by Balai Pustaka. This dictionary is the primary reference for the standard Indonesian language because ...

'', and the government's official elementary-school curriculum.

Historical

Apothecaries' ounce

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

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

The Spanish pound (

Spanish Spanish might refer to: * Items from or related to Spain: **Spaniards are a nation and ethnic group indigenous to Spain **Spanish language, spoken in Spain and many Latin American countries **Spanish cuisine Other places * Spanish, Ontario, Can ...

''libra'') was 460 g. The Spanish ounce (Spanish ''onza'') was of a pound, i.e. 28.75 g.

Tower ounce

The Tower ounce of was a fraction of the tower pound 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.

Ounce-force

An ounce-force is of a pound-force, or about . It is defined as the force exerted by a

of one avoirdupous ounce under standard gravity (at the surface of the earth, its

). 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

A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl.) is one of three units of

. An imperial fluid ounce is defined as 28.4130625 mL, a US customary fluid ounce is 29.57353 mL, and a US food labelling fluid ounce is 30 mL. The fluid ounce is sometimes referred to simply as an "ounce" in applications where its use is implicit, such as

bartending A bartender (also known as a barkeep, barman, barmaid, or a mixologist) is a person who formulates and serves alcoholic or soft drink beverages behind the bar, usually in a licensed establishment as well as in restaurants and nightclubs, but ...

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

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), 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.

Notes and references

External links

Dictionary of Units: Ounce
{{Authority control Customary units of measurement in the United States Imperial units Units of mass