Gold purity
24K, 22K, 21K and 18K gold purity explained
A clear guide to gold karat purity and estimating the pure-metal value contained in each gram.
Answer first
What should you remember?
- Karat measures gold content out of 24 parts.
- Raw metal value falls with lower purity.
- Hallmark, testing and invoice matter more than color alone.
What does karat mean?
Karat divides an alloy into 24 parts. 24K is near pure gold; 22K theoretically contains 22 parts gold out of 24, 21K contains 21, and 18K contains 18. Other metals add strength or change color.
Approximate purity percentages
Theoretical purities are about 99.9% for 24K, 91.7% for 22K, 87.5% for 21K and 75% for 18K. Local rules define tolerances and hallmarking, so check the product stamp or certificate.
Estimating metal value
Start with pure spot gold per gram and multiply by the purity ratio—for example 0.875 for 21K or 0.75 for 18K. This estimates metal value before fabrication, tax and margin.
Buying and verification
Verify hallmark, net metal weight, invoice and buyback policy. Stones may be included in total weight but are not repurchased at gold value. When uncertain, use professional testing rather than relying on a magnet or color alone.
Direct answers
Frequently asked questions
Is 24K always better?
It has the highest purity and metal value per gram but is softer. The right choice depends on investment, daily wear, design and cost.
How much gold is in 21K?
Theoretically 21 parts out of 24, or 87.5% gold, subject to local standards and hallmarking.