Ounce

This article is about the unit of mass. For the unit of volume, see Fluid ounce. For all other uses, see Ounce (disambiguation).

An ounce (abbreviated oz; apothecary symbol: ℥) is a unit of mass used in some systems of measurement.

Whilst various definitions have been used throughout history, two remain in common use: the avoirdupois ounce equal to approximately 28.3 g and the troy ounce of about 31.1 g. The avoirdupois ounce is widely used as part of the United States customary and British imperial systems, but the troy ounce is now only commonly used for the mass of precious metals such as gold.

Etymology

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). The abbreviation oz came later from the cognate Italian word onza (now spelled oncia).

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 → ch).

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 different standards of mass.

Mass of ounce units

Variant	(grams)	(grains)
International avoirdupois ounce	28.349523125	437.5
International troy ounce	31.1034768	480
Apothecaries' ounce
Maria Theresa ounce	28.0668
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
Chinese metric ounce (盎司)	50
English Tower Ounce	29.16	450

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.

In the avoirdupois system, sixteen ounces make up a 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, but in the United Kingdom it is now only used informally, having ceased to be a legal unit of measure in 2000.

International troy ounce

Main article: 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
• 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)

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.

Historical

Apothecaries' ounce

The obsolete apothecaries' ounce (abbreviated ℥) equivalent to the troy ounce, was formerly used by apothecaries (now called pharmacists or chemists).

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

Further information: Spanish customary units

The Spanish pound (Spanish libra) was 460 g. The Spanish ounce (Spanish onza) was ​¹⁄₁₆ of a pound, i.e. 28.75 g.

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.

Ounce-force

Main article: Pound-force

An ounce-force is ​¹⁄₁₆ of a pound-force, or .

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

Main article: 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.

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

External links

• Dictionary of Units: Ounce