What does 24 karat, 22 karat or 21 karat gold means?

We hear about jewellers or gold traders selling 24 karat, 22 karat gold coins or 20 karat, 18 karat gold jewllery and so on. The first thing that always comes to our mind is 'What exactly does this 24, 22 or 21 karat really means?'.

24 karat simply means that the gold is 99.90% pure or higher, so the maximum amount of impurities (other metal) it may contain is 0.10% or less. Similarly 22 karat gold will contain 91.60% pure gold alloyed (mixed) with other metals like silver, copper, etc.

Understanding further, gold jewellery cannot be made in 24 karat gold as the purest form of gold is not hard enough to make wearable jewellery and may break easily. Hence some more amount of other metals are added to gold to make it strong enough for gold jewellery. Adding these other metals to gold reduces the purity of gold and we start hearing about gold jewellery or gold coins made in 21 karat, 20 karat, 18 karat and more below.

So, how pure is my gold? Below is the table explaining karat against gold purity percentage based on Indian Hallmark standards.