Online Tool Store
Metal Purity Converter
Convert gold, silver, and platinum purity between karat, millesimal fineness, and percentage notation, with standard hallmark presets and alloy composition breakdown.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Millesimal Fineness Hallmark
Parts pure metal per 1,000
Karat Equivalent
Based on 24 parts standard
Pure Metal Percentage
Precious Metal Purity Hallmark Conversion Chart
| Karat Stamp | Millesimal Fineness | Pure Content % | Common Applications |
|---|
How it works
- Select the precious metal type (Gold, Silver, or Platinum).
- Choose your input notation (Karat out of 24, Millesimal Fineness out of 1,000, or Percentage %).
- Enter your purity value or select a standard hallmark preset (24K, 22K, 18K, 14K, 10K, 925 Sterling).
- The calculator converts the value across all precious metal standards, detailing exact pure metal fractions and alloy composition.
FAQ
What is the difference between Karat and Millesimal Fineness?
Karat measures gold purity in 24 parts (e.g. 18k = 18/24 = 75% gold). Millesimal Fineness expresses precious metal purity in parts per 1,000 (e.g. 750 gold, 925 sterling silver, 950 platinum), which is the global legal standard for jewelry hallmarks.
Why is 24K gold rarely used for everyday jewelry?
Pure 24K gold (99.9% fine) is extremely soft and easily bends, scratches, and deforms. Alloying it with stronger metals like copper, silver, nickel, and zinc (creating 18K or 14K gold) provides essential scratch resistance and structural durability for gemstones.
What is 925 Sterling Silver?
Sterling Silver contains 92.5% pure silver and 7.5% alloy (typically copper), stamped with the international "925" hallmark to ensure hardness for jewelry and silverware.
What are the legal minimum gold karat standards by country?
The United States requires a minimum of 10K (417 fineness) to be legally labeled and sold as gold jewelry, whereas the United Kingdom and Australia recognize 9K (375 fineness).
How we compare
| Feature | Online Tool Store | Jewelry hallmark stamp charts | Pawn shop scratch tests |
|---|---|---|---|
| Simultaneous Karat, Fineness, and % conversion | ✓ | Fixed charts only | ✗ |
| Alloy weight fraction and composition breakdown | ✓ | ✗ | ✗ |
| Gold, Silver, and Platinum hallmark standards | ✓ | ✓ | ✓ |