Reading Diamond Certs :: Depth %

Depth % is the ratio of the total depth of the diamond (from table to culet) as compared with the total diameter, or girdle diameter.


For instance, if the total diameter of a round diamond is 6.00 mm and the total depth is 4.00 mm, then the depth percentage is 66.7%.

The ranges that are commonly considered best for each shape vary quite a bit, so we will just give the basic dimensions for rounds here. Dimensions for other shapes are beyond the scope of this brief report.

However, for the most part, the brilliant cuts other than the round also follow similar guidelines given below. Other “brilliant cuts” include the pear, marquise, oval, and heart.

  • Excellent = 60.1 – 62%
  • Good = 62 – 64%
  • Fair = 64 – 66%
  • Poor = over 66% or under 60%

For fancy shapes like the princess, radiant and emerald cuts, allow up to 70 – 75% for acceptable ranges (in my opinion).

All of this depends of course, on how everything else works together, and combinations create a huge variation of acceptable and even premium light performance.

To really know how a diamond performs, this is one example of when it is crucial to trust in the overall Cut Grade, and not pay too much attention to the individual numbers like Depth %. I will give a great example in the next lesson, in the Table %.

Now move on to the next lesson :: Table %

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