You're familiar with the gold standard, where 24k = 100%.
The platinum standard is based on parts per thousand, where 1000 parts = 100%. All platinum alloys are derived from this standard. The two most common platinum alloys found in the US.
95% Platinum: This alloy is 950 parts per 1000 and 50 parts other metals. Common quality marks are: Platinum, Plat, Pt, Pt950, 950Pt, 950Plat and Plat950.
90% Platinum: This alloy is 900 parts per 1000 and 100 parts other metals. Common quality marks are: 900Pt, Pt900, and 900Plat.
The platinum standard is based on parts per thousand, where 1000 parts = 100%. All platinum alloys are derived from this standard. The two most common platinum alloys found in the US.
95% Platinum: This alloy is 950 parts per 1000 and 50 parts other metals. Common quality marks are: Platinum, Plat, Pt, Pt950, 950Pt, 950Plat and Plat950.
90% Platinum: This alloy is 900 parts per 1000 and 100 parts other metals. Common quality marks are: 900Pt, Pt900, and 900Plat.