Grams, ounces and troy ounces — the precious-metal weight trap
An avoirdupois ounce is 28.35 g. A troy ounce is 31.10 g. Precious metals use troy — and the 10% gap has funded generations of shady dealers.
Two ounces coexist in modern commerce. The avoirdupois ounce weighs your groceries, your baby and your postage. The troy ounce weighs your silver spoons and gold coins. They are not interchangeable, and the difference is exactly the margin a dishonest buyer needs to underpay by 10% on a bullion trade.
The exact factors
1 avoirdupois oz = 28.349523125 g (exact) > 1 troy oz (ozt) = 31.1034768 g (exact) > 1 troy oz = 1.09714 avoirdupois oz > 1 troy pound = 12 troy oz = 373.24 g (not 16 troy oz — troy pounds have 12 ounces)
Why two ounces
The avoirdupois system was designed for bulk commodities and standardised in England in 1959. The troy system, named after Troyes in France, was the medieval money weight — kept for precious metals because refined-metal accounting predated the avoirdupois system. Every LBMA gold bar today is weighed in troy ounces to the second decimal.
Worked example — a 1 oz gold Krugerrand
A Krugerrand is 'one troy ounce of fine gold' — 31.1035 g of pure gold. But the coin itself weighs 33.93 g because it is alloyed with 8.33% copper for durability. Buyers pay by the gold content (troy ounce), not the coin's total weight. Confusing the two is the classic beginner mistake.
Silver flatware and hallmarks
US sterling silver is 92.5% pure. A 100 g silverware set contains 92.5 g = 2.975 troy oz of silver. UK antique silver is often stamped with the weight in troy ounces and pennyweights (dwt) — 1 dwt = 1/20 troy oz = 1.555 g.
The five-second recap
Precious metals: troy ounces (31.10 g). Everything else: avoirdupois (28.35 g). Never let a dealer weigh your gold on a kitchen scale.
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FAQ
How many grams in a gold sovereign?+
7.98805 g total weight, containing 7.322 g (0.2354 troy oz) of pure gold.
What is a pennyweight?+
20 pennyweights (dwt) = 1 troy oz. So 1 dwt = 1.555 g. Still used in jewellery.
Are diamonds weighed in troy ounces?+
No — diamonds and gemstones use carats. 1 carat = 0.2 g exactly.
This article was written by The Turbo Unit Converter engineering desk (Precious metals metrology) and last reviewed on 2026-06-28 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.