BetterThanDiamond.com AnswerBase

Carat refers to the weight of a gemstone and mm (millimeter) refers to its physical measurements.

Due to differences in the specific gravity (the ratio of the weight or mass of a given volume of a substance to that of another substance (usually water for solids and liquids)) used as a standard among different gemstones, a 1 carat gem may be a larger (i.e. opal, which weighs less) or smaller (i.e. corundum or CZ, which weigh more) mm size than a 1 carat diamond (approx. 6.5mm).

Due to the fact that the same mm size may be a different carat (weight) depending on the type of gem used, most ready-made mountings are manufactured and calibrated for specific mm sizes of gemstones, and many gemstones are cut and calibrated to fit specific mm sizes of heads/prongs rather than cut for the carat weight of the stone.

The Asha carat weights on the ‘Asha Diamond Simulant’ pages have been converted to and are listed in diamond weight.