The purity of gold is measured in Karat (K). Although the purest form of gold is available in 24 K, it is quite soft and not durable to make ornaments. So in order to make it durable and long lasting, certain percentage of other metals like copper, nickel, silver and zinc are blended along-with gold. The karat vary from 10K to 12, 14, 18, 22, and 24K. Basically more the karat weight increases the purity of the gold increases too. For instance 18K have 75% of gold in it while 14K have 58% of gold in it. A unit karat of gold is equal to 1/24 part (4.1667%). Pure 24K gold is expensive and also not recommended to be worn because of its lack of durability and so gold is mixed with other durable metals.
To study the percentage of gold and other metals take a look at the table below.The gold karat chart shows how many parts of gold and how many parts of other metals is used for gold jewelry.