Ounce (oz)

US & ImperialCurrent unit

One sixteenth of a pound, exactly 28.349523125 g. Used for food, mail and consumer goods in the US and UK.

1 ounce = 0.02834952313 kilograms (approximately).

About the ounce

A twelfth part is what ounce originally meant. It comes from the Roman uncia, one twelfth of the Roman pound, a word that also gave English the inch. The abbreviation oz does not come from English at all but from the Italian onza or oncia. Over the centuries many regions and trades used different ounces: the English Tower ounce of 29.16 g was abolished by Henry VIII in 1527, and the Dutch ons was redefined as exactly 100 g in 1820.

The avoirdupois ounce used for everyday goods is one sixteenth of a pound, exactly 28.349523125 g or 437.5 grains, the standard in the US and under the UK imperial system. It is not the same as the troy ounce for precious metals, and neither is the fluid ounce, which measures volume. Ounces still describe portions such as steaks and burgers, and they show up in unexpected places: fabric is graded by weight per area, so a 16 oz denim is a heavy cloth, and the copper on a circuit board is specified in ounces, where 1 oz is roughly 34.7 micrometres thick.

Sources: Wikipedia: Ounce; NIST Guide to the SI, Appendix B.8 (mass conversions)

Ounce conversion chart

1 ounce expressed in every other weight & mass unit:

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• pound (weight & mass)
• grain (weight & mass)
• dram (weight & mass)
• inch (length)
• foot (length)
• yard (length)
• mile (length)
• thou (length)
• league (length)
• furlong (length)
• chain (length)
• rod (length)
• link (length)
• hand (length)
• cubic inch (volume)
• cubic foot (volume)

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