Karat is a term used to indicate gold purity. In many countries it is a legal standard to stamp gold jewelry with markings such as 10KT, 14KT and 18KT. The Karat stamp indicates the purity of the metal. Pure gold is 24 karat so the number preceding the KT marking indicates how many parts out of 24 are pure gold. For example 14KT indicates that there are 14 units of pure gold mixed with 10 units of other metal. These alloys are added to control durability, color and cost of fine jewelry.
Carat is a unit of weight used to measure diamonds and precious gemstones. In ancient times traders used carob seeds on balance scales to determine the weight of gemstones. As time passed the term carob evolved into the word carat and an exact weight was assigned. In modern times the carat is equal to 1/5 of a gram.