To use a Gold Calculator correctly, it is important to understand gold purity and weight. Gold purity tells how much pure gold is present in an item. The highest purity is 24K, which means almost 100% pure gold. However, pure gold is very soft, so it is rarely used for jewelry. Most jewelry is made of 22K or 18K gold. 22K gold contains about 91.6% pure gold, while 18K gold contains about 75% pure gold. The remaining part is made of other metals to make the jewelry strong and durable. A Gold Calculator adjusts the value based on this purity difference.