A 2-carat diamond has a width of 8.2 mm in the round brilliant cut. However, it is important to remember that 2-carat diamonds with different cuts typically have differing size measurements.
For example, a 2-carat diamond with a princess cut is only 7.5 mm in width. This is because a shallow cut, such as the round brilliant, has a greater diameter than a deep cut. The carat is a measurement of weight that is used only for diamonds and gemstones. The size of a 2-carat diamond would be different than a ruby of the same weight because the two stones have different densities.