Look closely at almost any piece of gold and you will find a set of tiny stamps — the hallmarks. They are not decoration; they are a certificate in miniature, telling you the purity of the metal and, in many countries, who made it and where it was tested. Learning to read them is the single most useful skill for anyone buying gold, because purity is what sets value.
Millesimal fineness: the universal number
The most reliable mark worldwide is the millesimal fineness — the parts of pure gold per thousand. “999” means 99.9% pure (24K), “916” is 22K, “875” is 21K, “750” is 18K, “585” is 14K, and “375” is 9K. Because it is a plain number rather than a regional term, fineness travels across borders: a “750” stamp means 18-karat gold whether you are in Milan, Mumbai, or Manchester. Our full gold purity chart lists every common grade side by side.
Karat stamps
Alongside (or instead of) fineness, many markets stamp the karat directly: 24K, 22K, 18K, 14K, 10K, or 9K. This is common in the United States and much of Asia. Karat and fineness say the same thing two ways — 22K and “916” are identical — so seeing both simply double-confirms the purity.
Country hallmark systems
Some countries add a compulsory, government-backed hallmark that carries extra information. The United Kingdom requires a full hallmark — fineness, the maker’s sponsor mark, the assay-office mark, and a date letter for the year. France stamps 18K with its distinctive eagle’s-head punch. India’s BIS system adds a 6-character HUID you can verify in an app. Italy includes a province number identifying the manufacturer. Our country guides for the UK, France, India, and Italy explain each in detail.
How to verify a hallmark
Use a loupe or magnifier to read the marks clearly, and check that the stamped fineness matches what the seller claims. Where a national register exists — like India’s BIS Care app — use it. For anything valuable or second-hand, buy from a reputable dealer, and if in doubt, a jeweler can perform an acid or electronic purity test in minutes. Be wary of items with no marks at all, or with marks that look crude or inconsistent.
Why it matters so much
The gap between purities is large: 22K gold contains roughly 22% more gold than 18K, and far more than 9K. Paying a 22K price for an 18K piece is a costly mistake that a five-second look at the hallmark prevents. Once you know the purity, our converter shows exactly what the metal is worth by weight, and understanding gold karats explains which purity suits which use. This article is educational and not financial advice.