Avoirdupois Ounce
Also: av. oz, commercial ounce, avoirdupois ounce
Weighing exactly 28.349523125 grams, the avoirdupois ounce (av. oz) is the everyday mass unit of the Anglo-American world — and it sits noticeably below the 31.1035-gram troy ounce that governs the precious-metals trade.
When people in English-speaking countries weigh groceries, toiletries or ordinary merchandise, the unit behind the figure is usually the avoirdupois ounce (written av. oz or oz av.). Its name traces back to the medieval Franco-English commercial vocabulary — avoir de pois, meaning "goods of weight" — and its value has been fixed consistently ever since Britain's Weights and Measures Act of 1824. To translate it into grams, troy ounces or other units, the unit converter does the job in seconds.
Watch out: avoirdupois versus troy
The moment precious metals enter the picture, the troy ounce (ozt) becomes a source of dangerous confusion. Belonging to the troy weight system, the troy ounce is the worldwide reference for gold, silver, platinum and palladium — and it outweighs the avoirdupois ounce by roughly 10 %:
| Unit | Grams | Grain |
|---|---|---|
| Troy ounce (ozt) | 31.1035 g | 480 gr |
| Avoirdupois ounce (av. oz) | 28.3495 g | 437.5 gr |
| Difference | −2.754 g | −42.5 gr |
Weigh silver jewellery, scrap silver or broken gold in avoirdupois ounces and then price it off the silver price, and you will end up short-changing yourself — the value comes out too low. The conversion you need is:
Troy ounces = avoirdupois ounces × 0.911458
Converting to familiar units
- 1 av. oz = 28.349523125 g (exact, legally defined)
- 1 av. oz = 0.9115 ozt (troy ounces)
- 1 av. oz = 437.5 grain
- 1 kilogram = 35.274 av. oz
When the avoirdupois ounce turns up in metals
The professional metals market quotes only in troy ounces — that goes for the gold price and for COMEX alike. Even so, private buyers and sellers bump into the avoirdupois ounce in a handful of everyday scenarios:
- Buying jewellery: jewellers across the USA and the UK occasionally put gold jewellery on the scale in av. oz.
- Imported scales: cheap kitchen scales shipped in from outside the EU tend to show a bare "oz" with no qualifier — that "oz" is the avoirdupois ounce.
- Online marketplaces: US listings state weights in oz av., so in the melt value calculator make a point of picking the right unit.
In brief
Coming in nearly 9 % lighter than the troy ounce, the avoirdupois ounce has no standing in the precious-metals trade. To turn an everyday weight into a metal value without tripping over a miscalculation, always run it through the factor 0.9115 — or simply reach for the unit converter.