Diamonds are measured by carat weight. A carat weighs 200 milligrams. If a diamond is referred to as four grains, this also means that it is a carat diamond. Carat The word comes from the word carob. A carob is a bean that grows on a tree in the Mediterranean. In the past, if a diamond weighed the same as a carob bean, it was one carob, or a carat.
However, in the far east, where Carob trees do not grow, rice was used to measure the weight of a diamond. If a diamond weighed up to four grains of rice, it was four grains – a carat as we know at now. The majority of purchases of diamonds are diamonds that are 1/3 of a carat.
Beware when shopping for diamonds that are already established or mounted. If more of a diamond is used in the room, the tag on the jewelery will give the CTW or Carat Total Weight – it does not tell you the weight in carats each stone in the room. You should ask the jeweler for carat total weight diamond largest in the room to truly understand what you are buying.