Platinum Purity Marks Explained

What stamps like 999, Pt950, Pt900, and Pt850 actually mean.

Platinum jewelry is stamped with a small mark showing purity, usually as a percentage out of 1000 parts, often prefixed with “Pt.” Here’s how to read the marks you’re most likely to find.

Common fineness marks

999 — pure platinum, 99.9%, mainly used for bars and coins
Pt950 — 95% pure, the most common standard for platinum jewelry
Pt900 — 90% pure, also common in fine jewelry
Pt850 — 85% pure, a lower but still legitimate platinum standard

See the full Platinum Fineness Guide for the exact purity and typical uses of each mark.

Don’t confuse it with white gold

A piece marked 14k or 18k, even if it looks silvery-white, is white gold — a gold alloy with a white-metal plating — not platinum. Only marks like 999, Pt950, Pt900, or Pt850 indicate actual platinum content.

The Platinum Calculator is designed for solid platinum items marked with one of these purities.

Frequently asked questions

What does Pt900 mean on a ring?

Pt900 means the ring is 90% pure platinum, alloyed with 10% other metal — a common purity standard used alongside Pt950 in fine jewelry.

Is a ring stamped 'Plat' the same as Pt950?

'Plat' or 'Platinum' alone confirms the metal but not the exact purity — look for an accompanying number like 950 or 900, or have it tested to confirm the specific fineness.