1 carat diamond is said to be 200 milligrams or one-tenth of 1 gram. 1 carat is the unit used for the weight of a diamond. The dimensions of a 1 carat diamond depend on its size, cut and clarity. Usually the diameter of 1 carat diamond is between 6.5mm to 7mm. Higher quality diamonds tend to be more expensive than lower quality diamonds (eg diamonds with higher colour, size and clarity are more valuable). Visit our online store for more information and to purchase 1-carat diamonds.