The ounce () is any of several different units of

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

weight In science and engineering, the weight of an object is a quantity associated with the gravitational force exerted on the object by other objects in its environment, although there is some variation and debate as to the exact definition. Some sta ...

, or

volume Volume is a measure of regions in 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) ...

and is derived almost unchanged from the , an Ancient Roman unit of measurement. The

avoirdupois ounce The ounce () is any of several different units of mass, weight, or volume and is derived almost unchanged from the , an Ancient Roman unit of measurement. The avoirdupois ounce (exactly ) is avoirdupois pound; this is the United States cu ...

(exactly ) is

avoirdupois pound The pound or pound-mass is a unit of mass used in both the 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 lega ...

; this is the United States customary and British imperial ounce. It is primarily used in the United States. 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 the Kingdom of England in the 15th century and is primarily used in the precious metals industry. The troy weight units are the grain, the pennyweight (24 grains), the troy ounce (20 p ...

' of exactly is used instead for the mass of

precious metal Precious metals are rare, naturally occurring metallic chemical elements of high Value (economics), economic value. Precious metals, particularly the noble metals, are more corrosion resistant and less reactivity (chemistry), chemically reac ...

s such as gold, silver, platinum, palladium, rhodium, etc. The term 'ounce' is also used in other contexts: * The

ounce-force The pound of force or pound-force (symbol: lbf, sometimes lbf,) is a unit of force used in some systems of measurement, including English Engineering units and the foot–pound–second system. Pound-force should not be confused with poun ...

is a measure of

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

(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 S ...

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 (meaning: a twelfth), a unit in the

Ancient Roman units of measurement The units of measurement of ancient Rome were generally consistent and well documented. Length The basic unit of Roman linear measurement was the ''pes'' (plural: ''pedes'') or Roman foot. Investigation of its relation to the English foot goes ...

weighing about 27.4 grams or 96.7% of an avoirdupois ounce, that was one-twelfth () of the

Roman pound The units of measurement of ancient Rome were generally consistent and well documented. Length The basic unit of Roman linear measurement was the ''pes'' (plural: ''pedes'') or Roman foot. Investigation of its relation to the English foot goes ...

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

Old English Old English ( or , or ), 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 developed from the languages brought to Great Britain by Anglo-S ...

, becoming in Old English, which survives in modern English as ''

inch The inch (symbol: in or prime (symbol), ) is a Units of measurement, unit of length in the imperial units, British Imperial and the United States customary units, United States customary System of measurement, systems of measurement. It is eq ...

''; 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 pe ...

through Anglo-Norman and

Middle French Middle French () is a historical division of the French language that covers the period from the mid-14th to the early 17th centuries. It is a period of transition during which: * the French language became clearly distinguished from the other co ...

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

cognate In historical linguistics, cognates or lexical cognates are sets of words that have been inherited in direct descent from an etymological ancestor in a common parent language. Because language change can have radical effects on both the s ...

, pronounced (or later , 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.

Active 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: Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States ...

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

Commonwealth of Nations The Commonwealth of Nations, often referred to as the British Commonwealth or simply the Commonwealth, is an International organization, international association of member states of the Commonwealth of Nations, 56 member states, the vast majo ...

. In the

avoirdupois Avoirdupois (; abbreviated avdp.) is a measurement system of weights that uses pounds and ounces as units. It was first commonly used in the 13th century AD and was updated in 1959. In 1959, by international agreement, the definitions of the p ...

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 le ...

; 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 an independent unit of measure in 2000, but may still be seen as a general 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 obsolete

troy pound Troy weight is a system of Physical unit, units of mass that originated in the Kingdom of England in the 15th century and is primarily used in the precious metals industry. The troy weight units are the Grain (unit), grain, the pennyweight (24 ...

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

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

platinum Platinum is a chemical element; it has Symbol (chemistry), symbol Pt and atomic number 78. It is a density, dense, malleable, ductility, ductile, highly unreactive, precious metal, precious, silverish-white transition metal. Its name origina ...

palladium Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas (formally 2 Pallas), ...

rhodium Rhodium is a chemical element; it has 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 isot ...

silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...

Bullion coin A bullion coin (also known as a specie) is a coin struck from highly refined precious metal (bullion) and kept as a store of value or an investment rather than used in day-to-day commerce, or collectable, with numismatic value beyond that of its ...

s are the most common products 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 hard ...

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 in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

material)

Metric ounces

Some countries have redefined their ounces in the

metric system The metric system is a system of measurement that standardization, standardizes a set of base units and a nomenclature for describing relatively large and small quantities via decimal-based multiplicative unit prefixes. Though the rules gover ...

. 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 or Nederlands commonly refers to: * Something of, from, or related to the Netherlands ** Dutch people as an ethnic group () ** Dutch nationality law, history and regulations of Dutch citizenship () ** Dutch language () * In specific terms, i ...

, ''ons'') as 100

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

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 Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

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 the Language Development and Fostering Agency and published by Balai Pustaka. This dictionary is the primary reference for the standard Indonesian language beca ...

'', 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 ''Apothecary'' () is an archaic English term for a medical professional who formulates and dispenses '' materia medica'' (medicine) to physicians, surgeons and patients. The modern terms ''pharmacist'' and, in British English, ''chemist'' have ...

, 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 The Maria Theresa thaler (MTT) is a silver bullion coin and a type of Conventionsthaler that has been used in world trade continuously since it was first minted in 1741. It is named after Maria Theresa who ruled Austria, Hungary, Croatia and ...

, 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 () was 460 g. The Spanish ounce (Spanish ) was of a pound, i.e. 28.75 g. It was further subdivided into 16 (each 1.8 grams). For pharmaceutical use, the Greek was used, subdividing the Spanish ounce into 8 (3.6 grams), due to being equivalent to of an avoirdupois ounce. In either case, it could be further subdivided into

, each one 49.9 milligrams.

Tower ounce

The Tower ounce of was a fraction of the

tower pound The pound or pound-mass is a unit of mass used in both the 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 le ...

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 avoirdupois ounce under

standard gravity The standard acceleration of gravity or standard acceleration of free fall, often called simply standard gravity and denoted by or , is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. It is a constant ...

(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 a unit of

. An imperial fluid ounce is defined in British law as exactly 28.4130625

millilitre The litre ( Commonwealth spelling) or liter ( American spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metres (m3). A cu ...

s, while a

US customary United States customary units form a system of measurement units commonly used in the United States and most U.S. territories since being standardized and adopted in 1832. The United States customary system developed from English units that ...

fluid ounce is exactly 29.5735295625 mL, and a US food labelling fluid ounce is 30 mL. The fluid ounce is sometimes referred to simply as an "ounce" in contexts where its use is implicit, such as

bartending A bartender (also known as a barkeep or barman or 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, b ...

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 A printed circuit board (PCB), also called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...

(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