Troy Ounce
The standard unit for weighing precious metals, equal to about 31.103 grams, heavier than a regular ounce.
The troy ounce is the traditional unit the world uses to weigh and price precious metals. It equals exactly 31.1034768 grams, which is heavier than the everyday avoirdupois ounce of about 28.35 grams, so the two are not interchangeable. International spot prices for gold, silver and platinum are quoted per troy ounce, and jewellers convert that figure into a per gram rate to price actual pieces.
Troy ounce versus the everyday ounce
The ounce used for food and post is the avoirdupois ounce, about 28.35 grams. The troy ounce used for precious metals is about 31.10 grams, so it is roughly ten percent heavier. Mixing them up understates a gold weight, which is why the metals trade sticks strictly to troy.
The troy system is old, tracing back to the medieval market town of Troyes in France, and it survived into modern bullion trading precisely because everyone agreed on it. Today it is the fixed reference for quoting metal prices worldwide.
- One troy ounce is 31.1034768 grams.
- The everyday avoirdupois ounce is about 28.35 grams.
- The troy ounce is roughly ten percent heavier.
- Spot prices for gold, silver and platinum use the troy ounce.
Converting to a per gram rate
Jewellery is sold by the gram, but the market quotes gold per troy ounce, so a conversion is needed. Divide the per troy ounce price by 31.1035 to get the price per gram of pure gold. If gold is quoted at 2,400 dollars per troy ounce, that is about 77.16 dollars per gram of pure 24K gold.
From there the purity fraction scales it to a working karat rate. Multiply the per gram pure gold price by 0.916 for a 22K rate or 0.75 for an 18K rate, and that per gram figure is what feeds the metal value of a finished piece.
- A troy ounce is about 31.1035 grams.
- It is heavier than the everyday avoirdupois ounce.
- Global metal prices are quoted per troy ounce.
- Divide the per ounce price by 31.1035 to get a per gram rate.
Troy Ounce, in short.
How many grams are in a troy ounce?
A troy ounce is exactly 31.1034768 grams, usually rounded to 31.1035 grams for calculations.
Why is precious metal weighed in troy ounces?
It is the long standing international standard for bullion, so gold, silver and platinum spot prices are all quoted per troy ounce, keeping trade consistent worldwide.
Related terms
See troy ounce inside a real jewellery system.
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