Carat represents the weight of a diamond. One carat equals 200 milligrams.
Carat weight of a diamond influences the price greatly. As the carat weight increases, the price goes up exponentially. A one carat diamond costs nearly four times more than four 0.25 carat diamonds.
Do not confuse carat weight of a single diamond with total carat weight of multiple diamonds in a piece of jewelry. Carat weight of multiple diamonds is often referred to "carat total weight" or "total carat weight".