ounce
Massexact by definition
The avoirdupois ounce is one sixteenth of an international pound, exactly 0.028349523125 kilograms. The value is exact because the pound was fixed at exactly 0.45359237 kg by the 1959 international yard and pound agreement.
Watch out: Three unrelated ounces share the word. The avoirdupois ounce here is 28.349523125 g. The troy ounce used for gold, silver and platinum is 31.1034768 g, about 10 percent heavier, which is why a bullion price quoted per ounce is never per this ounce. The fluid ounce is a volume, and even that comes in US (29.5735 mL) and imperial (28.4131 mL) sizes.
| 1 oz | 0.028349523 kg |
The name descends from the Latin uncia, a twelfth part, which is also the ancestor of the inch. The ounce kept the name after the avoirdupois system moved it to a sixteenth of a pound.