A karat is used to measure the value of gold, diamonds and other gems, and precious metals. Originally, a karat was the weight of a Mediterranean carob tree seed. However, there are two meanings today for the term karat.

The first is 200 milligrams, used to measure the weight of gemstones. This form of measurement is known as a carat. The second meaning is the purity, or amount of gold per 24 parts gold alloy. 24 karat gold, or 24k, is pure gold, while 18 karat gold is ¾ gold and so forth.