Here It's Brilliant Round Cut Moissanite Carat Weight (CT) and Moissanite Size (MM) Chart. Please Noted the actual measurements and carat weights may vary slightly depending on the specific manufacturer and cut of the Moissanite gemstone. Consequently, we favor using the millimeter (mm) measurements when talking about our vvs moissanite diamond sizes. Moissanite is often lighter than diamonds, so its size may appear slightly larger for the same carat weight.