One troy ounce equals exactly 31.1034768 grams — the unit used for gold worldwide, and heavier than the everyday ounce of about 28.35 g. To convert, multiply troy ounces by 31.1035 for grams, or divide grams by 31.1035 for troy ounces.
One troy ounce equals 31.1034768 grams, while the everyday (avoirdupois) ounce equals about 28.35 grams. The troy ounce is the international standard for weighing precious metals, and it is the unit behind every quoted gold price you see. If you weigh your jewellery on a kitchen scale set to ounces, you are using the wrong ounce and will underestimate the metal by roughly 10 percent. In France, dealers weigh in grams, but the reference spot price is published per troy ounce, so understanding the conversion lets you follow the same figure they do.
Multiply troy ounces by 31.1035 to get grams; divide grams by 31.1035 to get troy ounces. Because French buyers price in grams, the conversion matters mainly when you want to check a spot price against a weighed piece. To do that, take the public spot price per troy ounce, divide it by 31.1035 to get the price of pure gold per gram, then adjust for fineness. For example, an 18-karat piece is 750 thousandths pure, so only three-quarters of its weight is gold. Half a troy ounce is 15.55 g; a quarter is 7.78 g. Coins and bars are often sold in troy-ounce denominations, while broken jewellery is always weighed in grams.
A gram of gold is only worth its pure-gold content, and fineness tells you how much of that gram is actually gold. French and international hallmarks use thousandths: 24k = 999, 22k = 916, 18k = 750, 14k = 585, 9k = 375. An 18k gram therefore contains 0.750 g of pure gold, a 9k gram only 0.375 g. Weight, hallmark, spot price and fineness together set the metal value; condition and any numismatic premium can add to collectible coins. What the spot price does not tell you is the buyback rate: dealers all see the same public spot, but each keeps a different margin, and they need not publish it. That margin, not the ounce-to-gram maths, is where offers really diverge. Compare gold buyers in your city to see who pays the higher percentage.
In France, selling gold triggers strict traceability rules regardless of the unit used. Payment must be traceable: the buyer pays by bank transfer or cheque, never in cash. You must show valid ID, and the transaction is recorded in a mandatory police register. On tax, you normally choose between a flat tax on precious metals applied to the sale price, or the capital-gains regime if you can prove your original purchase with an invoice. Weighing should happen in front of you on a scale showing grams to two decimals, so you can apply the conversion yourself and check the fineness-adjusted figure against the day's spot.
Yes. A troy ounce is 31.1035 g against about 28.35 g for the standard avoirdupois ounce, roughly 10 percent heavier. Always use the troy ounce for gold, silver and platinum.
Half a troy ounce is 15.55 g and a quarter is 7.78 g. These figures refer to total weight; the pure-gold content depends on fineness, so an 18k half-ounce holds 750 thousandths of that weight in gold.
French dealers weigh in grams, usually to two decimals, and price per gram. The troy ounce only appears in the public spot price, which you can divide by 31.1035 to get the pure-gold value per gram.