The carat is the traditional unit of measurement for a diamond’s weight. Moissanite is not measured in carats because it weighs approximately 10 percent less than diamond. For example, a 6.5mm round diamond would weigh 1.0ct, while a 6.5mm round moissanite would weigh 0.88ct. The two stones would be the same size – 6.5mm in diameter. All stones for sale are listed with their size in millimeters and the diamond equivalent weight (DEW) in carats.