Diamonds are measured in Carat Weight. One carat weighs 200 milligrams. If a diamond is referred to as four grains, this also means that it is a one carat diamond. The word Carat comes from the word carob. A carob is a bean that grows on a tree in the Mediterranean. In times past, if a diamond weighed the same as a carob bean, it was one carob, or one 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 as much as four grains of rice, it was four grains - or one carat as we know it to be now. The majority of diamond purchases are for diamonds that are 1/3 of a carat.Beware when shopping for diamonds that are already set or mounted. If more than one diamond is used in the piece, the tag on the jewelry will give the CTW or Carat Total Weight - it does not tell you the carat weight of each stone in the piece. You need to ask the jeweler for the total carat weight of the largest diamond in the piece to truly understand what you are buying.
Diamond Grading Reports
You've been told that having a certificate or a diamond grading report is important, and as a responsible consumer, you get one - unfortunately, you probably won't understand a word of what is on that diamond grading report, unless you are a jeweler.
On the color grading scale, D, E, and F mean that the diamond has no color. G, H, and I means that it has very little color. J, K, and L means that the diamond has a slight yellow color. P, Q, R, S, T, U, V, W, and X means that the diamond is a darker shade of yellow. Z means that the diamond has a fancy color - other than white or yellow. On the color grading scale, D is the most valuable, and X is the least valuable - however diamonds that get a Z rating are the rarest and most expensive diamonds in the world.
There are many aspects to a grading report. Figuring it all out can be very confusing. You should talk to a jeweler you trust, and have them explain everything on the diamond grading report to you.