Diamond Carat Weight
Carat weight is the weight of the diamond measured in carats. One carat is divided into 100 "points," so that a diamond of 75 points weighs 0.75 carats. Carat weight is the most obvious factor in determining the value of a diamond. However, two diamonds of equal carat weights can have very different prices, depending on their quality. Diamonds of high quality can be found in all size ranges.
The scale above depicts the carat weights and diameter sizes of round diamonds. Other diamond shapes will vary. For example, while a 1 carat round shape diamond is 6.5mm on average, a 1 carat princess shape diamond is often 5.5mm instead.
Since diamonds are measured by carat weight, and not size, two diamonds of the same weight could have different sizes. Why? If a diamond is cut too shallow it will have a larger diameter but a smaller depth. Likewise, if a diamond is cut too deep (or bottom heavy) it will have a smaller diameter and thus appear smaller when viewed from the top.