Ounce
A unit of mass, weight, or volume from Roman times.
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The ounce is a unit of mass, weight, or volume that traces its origin to the Ancient Roman uncia, a term meaning "a twelfth." The uncia was one-twelfth of the Roman pound and weighed approximately 27.4 grams. The word itself was borrowed into English twice: once into Old English, where it became the word for "inch," and again through Anglo-Norman and Middle French, yielding the modern term "ounce." The abbreviation "oz" derives from the Italian cognate onza.
Active use
The most common modern form is the international avoirdupois ounce, defined as exactly 28.349523125 grams under the 1959 international yard and pound agreement. Sixteen of these ounces make an avoirdupois pound, and one ounce equals 437.5 grains. This unit remains a standard measure in the United States, though it was discontinued as an independent unit in the United Kingdom in 2000.
For precious metals like gold, silver, and platinum, the troy ounce is used instead. A troy ounce equals 480 grains, or exactly 31.1034768 grams, and twelve troy ounces make up the obsolete troy pound. Historically, a fine ounce referred to a troy ounce of pure gold content, while a standard ounce was a troy ounce of 22-carat gold.
Historical
Other historical definitions include the apothecaries' ounce, equivalent to the troy ounce, and the Tower ounce, which was used in English mints until it was replaced by the troy ounce in 1527. Some countries adopted metric equivalents: the Dutch redefined their ons as 100 grams, a usage that persists in Indonesia, and the German apothecaries' ounce was set at 30 grams. The Spanish ounce was 28.75 grams, and the Maria Theresa ounce, equal to 28.0668 grams, was used in Ethiopia. The term also applies to force and volume: the ounce-force is one-sixteenth of a pound-force, and the fluid ounce measures volume, with imperial and US customary versions differing slightly in millilitres.
Lore & Background
The ounce is a unit of mass, weight, or volume derived from the Ancient Roman uncia, which weighed approximately 27.4 grams and represented one-twelfth of the Roman pound. The term entered English through two borrowings: first into Old English as ynce (modern "inch"), and later via Anglo-Norman and Middle French, yielding "ounce." The abbreviation "oz" originates from the Italian cognate onza. Historically, many different ounces existed across jurisdictions, trades, and time periods, each with slightly varying standards. The most common modern version is the international avoirdupois ounce, defined as exactly 28.349523125 grams under the 1959 yard and pound agreement.
This ounce is a standard unit in the United States, while in the United Kingdom it ceased to be an independent measure in 2000 but remains a general indicator for portion sizes. The troy ounce, equal to 480 grains or 31.1034768 grams, is used exclusively for precious metals like gold, silver, platinum, palladium, and rhodium. Some nations redefined the ounce metrically: the German apothecaries' ounce was set at 30 grams, and the Dutch redefined their ons as 100 grams in 1820, a usage still common in the Netherlands and Indonesia.
The apothecaries' ounce, equivalent to the troy ounce, is now obsolete. Other historical variants include the Maria Theresa ounce (28.0668 g), the Spanish ounce (28.75 g), and the Tower ounce used in English mints until 1527. The ounce-force measures force, defined as the weight of one avoirdupois ounce under standard gravity. The fluid ounce is a volume unit, with imperial and US customary definitions differing slightly.
Reader's Guide
The ounce has played a significant role in trade, commerce, and measurement systems across cultures. Its persistence from Ancient Rome to modern times illustrates the continuity of measurement standards. The avoirdupois ounce remains crucial in the United States for everyday mass measurements, while the troy ounce is indispensable in the precious metals market. The fluid ounce, a separate unit of volume, is used in both imperial and US customary systems for liquids.
The ounce-force, derived from the avoirdupois ounce, is used in engineering. Additionally, the ounce is applied in specialized contexts such as fabric weight (areal density) and copper layer thickness on printed circuit boards. Despite the global shift toward the metric system, the ounce endures in specific industries and regions, reflecting its historical and practical importance.
More in Units & Measurement
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Ounce (CC BY-SA 4.0).
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