One carat diamond (standard round diamond) has a diameter of 6.49 mm and a mass of 0.2 g. ..

The following figure shows the comparison table of the weight (carat) and waist diameter (millimeter) of standard round diamonds, which can be used to inquire the diameters of diamonds of different qualities.

Diamonds come in different shapes and sizes. A one-carat round diamond has a diameter of 6.49 mm, while the Princess Square diamond has a diameter of 5.5 mm.. Other shapes and diameters of a carat diamond are: emerald 5 mm, pear 5.5 mm, oval 6.5 mm, heart 6.5 mm, olive tip 5.5 mm and ruby 4.75 mm.

The following figure shows the contrast between the object and the hand (1ct = 1ct).

The word diamond comes from the Greek Adamas, which means hard and untamable. Known as the "king of gems", diamond is recognized as the most precious gem in the world and one of the most popular gems.

Diamonds are stones endowed with stories and emotions, with religious worship and awe, and are regarded as symbols of courage, power, status and dignity. "Diamonds last forever, but one lasts forever".