The list below represents thes diamond’s carat size (e.g 1.0 ct) related to it’s appropriate diameter (e.g. 6.5 mm) for sizes up to 5cts. The measurements are a general guide for diameters in well cut diamonds. Most well cut or excellent cut diamonds will have related diameters.
An Excellent or Ideal Cut Diamond
For example, a 1.00ct diamond, with excellent proportions, should have a diameter of approximately 6.5 mm.
A Deep Cut Diamond
If your 1.0ct measures 6.0 mm, it is likely a very deep diamond. The narrower the diamond’s diameter often means the deeper the diamond from top to bottom.
A Shallow Cut Diamond
If your diamond measures 6.8 mm, the your diamond is likely very shallow diamond. The wider the diamond’s diameter often means the shallower the diamond is from top to bottom.
As explained on this site, deep and shallow diamonds do not display the same brillance as an excellent cut diamond will display. Deep and shallow diamonds are worth less per carat than diamond of equal weight and quality that is of proper depth as shown above. That is why these millimeters measurements, among other factors, are very important in terms of beauty and value.