Donaldson R F Gold Purity & Alloy Calculator
Karat, fineness, and how much of a piece is actually gold versus other metal.
How this is worked out
Pure gold is 24 karat; any lower karat means the item is an alloy — gold mixed with other metals (commonly silver, copper or zinc) for strength or colour. Purity as a fraction is simply karat ÷ 24, and fineness (sometimes stamped inside a ring, e.g. "750") is that same fraction expressed in parts per 1000. Multiplying the item's total weight by its purity fraction gives the fine gold weight (the actual gold content); the rest is the alloy weight — the other metals making up the piece.
Frequently asked questions
What karats are common in jewellery?
9k, 14k, 18k and 22k are typical, varying by country and tradition — 18k (75% gold) is common in Europe for fine jewellery, while 22k and 24k are more common where very high purity is traditionally preferred.
Does this tool give a price?
No — this site's precious-metal tools never fetch or assume a live metal price; you always type in your own price per unit weight wherever one is needed.
Related tools: Troy Ounce, Pennyweight & Grain Converter, Unit Converter, Wholesale & Retail Price Calculator.
Source / Last verified: the international karat scale (24 karat = pure gold) and fineness (parts per 1000) are standard jewellery-industry conventions — read/checked 1 October 2026. Weight units (troy ounce, pennyweight, grain) use the exact values from NIST Handbook 44, Appendix C, and NIST's own "Precious Metals Conversion Information" reference sheet.