In the United States platinum jewellery generally contains anywhere from 85 to 95% pure platinum. By comparison, 18-karat gold is 75% pure gold and 14-karat gold is only 58% pure gold. If a piece of platinum jewellery is marked "Platinum" then it contains at least 95% pure platinum. Jewellery with 85 to 95% pure platinum is marked "950 Plat." or "950 Pt.", "850 Plat" or "850 Pt." etc. (The two and four letter abbreviation ; both are used for referring to platinum).

Jewellery containing at least 50% pure platinum and at least 95% platinum group metals (platinum, palladium, iridium, osmium, rhodium and ruthenium), is marked with the platinum content followed by the content of the other metal. For example: "600 Plat. 350 Irid. " Or "600 pt. 350 Ir." Jewellery containing less than 50% pure platinum content cannot be marked with the word "platinum" or any abbreviation thereof.