Platinum Purity Calculator
Platinum percent and alloy from fineness.
What it does
Platinum marks read in thousandths: Pt950 holds 95% platinum against 5% hardeners for wear. Fineness divides by ten into percent.
The tool above takes millesimal fineness. It returns platinum percent with the Pt mark and alloy share.
The default 950 reads 95% with 5% alloy. The 900 case reads 90% with 10%, and 999 reads 99.9%.
Fineness standards define precious metal marks in parts per thousand, matching this division exactly. Trade guidance repeats millesimal reading for descriptions and hallmarks.
Stamps invite trust but assays decide: fakes mark high while acid and XRF read true. Separate this millesimal ruler from gold karat parts.
How to use
- Type the fineness.
- Read platinum percent first.
- Read the Pt mark beside it.
- Read alloy last.
- Assay stamped bargains.
- Separate gold karat math.
Formula
- Pt
- Millesimal fineness, 500 to 1000.
- platinum%
- Platinum share by weight.
ISO 9202 sets precious metal fineness in parts per thousand matching this division for platinum marks. Jeweler guidance repeats the same millesimal reading for trade descriptions. Gold karat is the separate 24 part ruler.
Worked example
Example: Pt950 jewelry
Default: 950 fineness.
- Mark: Pt950 jewelry.
- Pure: 950 / 10 = 95% platinum.
- Parts: Pt950 millesimal mark.
- Alloy: 100 minus 95 = 5% alloy.
- Check: 900 reads 90 with 10% alloy.
- Tool shows 95% platinum, Pt950, 5% alloy.
Reference table
| Mark | Platinum | Alloy |
|---|---|---|
| Pt999 | 99.9% | 0.1% |
| Pt950 | 95% | 5% |
| Pt900 | 90% | 10% |
| Pt850 | 85% | 15% |
Limits
- Share math only.
- Alloy mix unread.
- Plating fools surface tests.
- Marks vary by country.
Common mistakes
- Reading fineness as karat.
- Trusting stamps blindly.
- Pricing by mark alone.
- Ignoring alloy metals.
- Testing plated surfaces.
Try it yourself
Quick checks. Answers sit tucked under each question.
900 fineness?
90% platinum with 10% alloy.
999 fineness?
99.9% platinum with 0.1% alloy.
1200 fineness?
Over 1000 exceeds pure: enter 500 to 1000.
Questions
Fineness to percent?
Divide by 10: 950 is 95%, 900 is 90%, 999 is 99.9%.
Alloy metals?
Iridium, ruthenium, and cobalt harden platinum for wear.
Karat too?
No, karat purifies gold while fineness marks platinum. This page marks.
Test stamps?
Yes, by assay: stamps lie on fakes, acid and XRF tell truth.
Why platinum?
Yes, dense and durable with patina over shine. Percentages decide value.
Tarnish?
Skin, sweat, and chemicals dull alloys while pure metal shrugs. Rinse after wear.