Gold purity is measured in karats (K), with 24K gold being 99.9% pure. Twenty-two karat gold contains 91.7% pure gold, 18K gold has 75%, 14K has 58.3%, and 10K contains 41.7% pure gold. The remaining portion in each type is mix of metals such as copper, silver or zinc. Notably, 24K gold is often used in gold coins and bars.