The gold price is published every day, but almost always in a unit we do not use: dollars per troy ounce. To know what a ring, a coin or a bar in your hand is worth takes three conversions: ounce to gram, dollars to euros, and pure gold to the purity of your piece.
Step 1: ounce to gram
The ounce used for precious metals is not the ordinary ounce but the troy ounce, equal to 31.1035 grams. To turn a price per ounce into a price per gram, divide by 31.1035.
Step 2: dollars to euros
The international price is set in dollars and must be converted at the current euro/dollar rate. Many sources already publish the price in euros per ounce, which saves this step. The most used reference is the price set twice a day in London (LBMA), although the spot price moves continuously while markets are open. We explain it in how the gold price is set.
Step 3: the carats of your piece
The quoted price is for pure gold. A piece of jewellery or an alloyed coin contains less gold per gram, and its metal value is found by multiplying by its purity:
| Carats | Fineness | Gold per gram of piece | Typical use |
|---|---|---|---|
| 24 | 999.9 thousandths | 100% | Investment bars and coins |
| 22 | 916.7 thousandths | 91.7% | Krugerrand, American Eagle |
| 18 | 750 thousandths | 75% | Jewellery in Spain |
| 14 | 585 thousandths | 58.5% | Jewellery elsewhere |
| 9 | 375 thousandths | 37.5% | Budget jewellery |
A worked example with round numbers
Using example figures, not today's quote: if an ounce of gold trades at 3,110 euros, a gram of pure gold is worth about 100 euros (3,110 divided by 31.1035). A gram of 18-carat gold contains 75% gold, so its metal value is about 75 euros. A 10-gram 18-carat chain therefore contains about 750 euros of gold at that moment's price.
"The price of a gram of gold is a reference, not what you will be paid. Between the two lies the buyer's margin, and it pays to know how much it is before signing."
Why you get less when selling jewellery
Whoever buys used gold has to melt and refine it, take on the purity risk and earn a margin. So they offer a percentage of the metal value, not 100%. That percentage varies a lot from buyer to buyer, so it is worth working out the gold value of what you are selling and comparing offers. There is a practical guide in selling gold in Valencia at a fair price.
Investment gold works in a similar way but with much smaller margins: you pay a premium over spot when you buy, and when you sell the buy-back price is close to spot, especially for a recognised piece with an invoice.
Frequently asked questions
How many grams are in an ounce of gold?
A troy ounce is 31.1035 grams. It is the standard unit for precious metals.
How do I know the carats of a piece of jewellery?
From the hallmark stamped on it: in Spain, 750 means 18 carat. If there is none or it is worn, a professional buyer can test it.
Why does the price per gram change every day?
Because gold trades continuously on international markets, and the euro/dollar rate also plays a part.
Is 18-carat gold investment gold?
No. To be VAT-exempt investment gold, bars must be at least 995 thousandths and coins at least 900. 18-carat jewellery is valued by its gold weight.
Is selling used gold taxed?
If you sell for more than it cost you, the difference is a capital gain for personal income tax (IRPF). See how much gold you can sell without declaring it.