Carat refers to the weight of the diamond. Diamonds and other gems are weighed in metric carats. A carat is divided into 100 points - just like cents in a dollar. The higher the carat-weight of the diamond the more rare and expensive the diamond will be. It confuses many consumers that a 2 carat diamond is twice the size of a 1 carat, but costs more than twice as much. Rarity plays a major role in pricing; larger diamonds are more rare. A large stone that is exceptional in all graded criteria is exceptionally unique and valuable.