La plupart des gens pensent que le carat fait référence à la taille réelle d'un diamant., alors qu’en fait il s’agit d’une unité de mesure standard qui définit le poids d’un diamant. Un carat équivaut à 200 milligrammes. La taille des carats est également exprimée en « points », avec un diamant d'un carat équivalent 100 points, a one-half carat diamond being 50 points, a three-quarter carat diamond being 75 points, et ainsi de suite. Larger diamonds are much rarer than smaller ones.
Since a carat is a unit of measure and not size, two diamonds of the same carat weight may appear to be different sizes depending on how the diamond is cut. Some diamonds will have extra weight on the bottom part — or pavilion — of the stone, and therefore appear smaller. A premium cut Canadian diamond is perfectly cut, and will appear larger than many diamonds of a heavier carat weight.
If size or carat weight is your most important attribute, (for many people it is very important) that is perfectly acceptable. You may want to also consider the other 3 Cs to make sure you understand your tradeoffs.