Carat weight is the traditional measuring unit of a diamond's weight. Moissanite is usually listed in millimeters as they are *just* slightly lighter in weight than diamonds. For example, a 6.5mm round diamond weighs 1.0 carat, while a 6.5mm round moissanite weighs 0.88 carat. The two stones would be the same size looking from the top down - 6.5mm in diameter. Crown height, table size and pavilion sizes will vary from one manufacturer to the next. All stones are listed with their actual size in millimeter (mm) and/or the diamond equivalent in carats.