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. But 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.

Cut is very important. A properly cut diamond will both yield a good face up size and sparkle well. For example, let's say you're interested in a 1.00ct round diamond. A poorly cut diamond that is bottom heavy may only have a diameter of say 6.1mm. So not only are you short changed on the face up size, but you get a diamond that was not cut to it’s full potential and thus does not sparkle like it should.

This is why it’s important not just to get the biggest diamond you can afford, but the best cut diamond as well.

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