Hallmarks 750 and 925: what the numbers mean
The number stamped on a piece states how many parts per thousand of it are pure precious metal, so 750 means eighteen carat gold at seventy five per cent purity and 925 means sterling silver at ninety two and a half per cent.
gelisted editorial team · Updated 15 August 2026
The short version
- 750 parts per thousand equals 18 carat and 585 equals 14 carat.
- Sterling silver contains 925 parts per thousand of pure silver.
- 18 carat gold has a density of about 15,5 grams per cubic centimetre.
- A magnet does not distinguish gold from brass but rules out iron cores.
Three small digits inside a ring carry all the economic information about the piece. Reading them takes 10 seconds with a loupe.
How the figure works
The millesimal system expresses how much of 1,000 parts is pure metal. A piece marked 750 has 750 parts gold and 250 parts of alloying metals, usually copper, silver, palladium or nickel. That system sits alongside the carat scale, where 24 carats is pure gold, so 18 carats is 18 parts of 24, which is 750 parts per thousand.
| Mark | Carats | Pure metal |
|---|---|---|
| 999 | 24 carat | 99,9 % gold |
| 916 | 22 carat | 91,6 % gold |
| 750 | 18 carat | 75 % gold |
| 585 | 14 carat | 58,5 % gold |
| 375 | 9 carat | 37,5 % gold |
| 925 | sterling silver | 92,5 % silver |
| 800 | low grade silver | 80 % silver |
| 950 | platinum | 95 % platinum |
Why almost nothing is pure gold
Twenty four carat gold is too soft for daily wear: it scratches and deforms easily. The alloy adds hardness and colour. Copper pulls towards red, silver towards pale yellow, palladium and nickel towards white. An 18 carat ring survives decades of daily wear, while a 22 carat one loses its shape within a few years if worn every day.
What is marked in Spain
Pieces in precious metals must carry the fineness mark stating the content and the responsibility mark of the maker or importer, plus the assay mark where applicable. Together they identify who stands behind the declared fineness. A piece with no mark at all is not necessarily false, since older and handmade items may carry none, but it does mean the content should be confirmed by assay.
X-ray fluorescence testing, which does not damage the piece, costs 15 € to 40 € and establishes the fineness accurately enough for a sale.
Checks you can make yourself
A magnet rules out pieces with an iron core, though gilded brass is not magnetic either. Density is a stronger indicator: 18 carat gold weighs about 15,5 grams per cubic centimetre and silver about 10,4, against 8,5 for brass. Weighing the piece and measuring its volume by water displacement catches many imitations before any laboratory is involved.
Frequently asked
+What does 750 mean on a piece of jewellery?
Eighteen carat gold, with 750 parts per thousand of pure gold and 250 of alloying metals.
+And 925?
Sterling silver, containing 92,5 per cent pure silver with the balance usually copper.
+Why is pure gold not used?
Because 24 carat gold is too soft and scratches and deforms with daily wear.
+Is an unmarked piece fake?
Not necessarily. Older and handmade items often carry no mark, but the fineness should be assayed.
+How is fineness checked without damage?
By X-ray fluorescence, a non-destructive test costing 15 € to 40 €.
Sources
- 1Boletín Oficial del Estado, BOE (August 2026)
- 2London Bullion Market Association, LBMA (August 2026)