Carat vs karat

This is short article just to clear the confusion, and use as a reference.

The term karat is used to define purity of gold. Pure gold is defined as 24 karat, or 24K, gold. However, pure gold is soft and unsuitable for jewelry making. Gold used in jewelry can be more correctly described as gold alloy and is usually 9K, 14K and 18K (12K is also used, but mostly for gold fill). 22K and 24K are used for gilding and plating. The proportion of gold in gold alloys is calculated as follows:

(karat weight/24) x 100%

For example: 14K gold has (14/24) x 100 = 58.3%

The term carat describes the weight of precious, and recently also semi-precious, stones.
1 carat = 0.2 gram. Different stones have different density, different stones of the same carat weight will be different in size. This difference is negligible for relatively small precious stones (gems), but will grow progressively for larger semi-precious stones. Thus, semi-precious stones are described mostly by size rather than carat, and sometimes by both.