One of the most important things to consider when looking for the best diamonds to buy is the diamond depth percentages. The diamond’s depth percentage is the ratio of the diamond’s diameter compared to the diamond’s total depth (the measurement of the table to culet). When diamonds are shallow, they have low depth percentages but when diamonds are deeper, their depth percentages are higher.
The Total Depth Percentage will show whether a diamond is overweight or underweight in relation to its diameter. When the average girdle diameter of the diamond has been obtained, then calculating the total depth percentage can follow. The total depth percentage of the diamond is determined by first measuring the gem from table to culet. The measurement is then divided by the average girdle diameter of the diamond, and then the resulting figure is multiplied by 100, then the final figure is rounded to the nearest tenth of a percent.
Average Girdle Diameter = 6.40mm
Table to Cutlet Measurement = 4.00mm
4.00mm divided by 6.40mm = 0.625
0.625 x 100 = 62.5
62.5 rounded to the nearest tenth = 62.5%
Diamonds are considered well-proportioned if their total depth percentage is approximately 60%. If the depth percentage of the diamond is below 55%, they are usually considered underweight. If the depth percentage of the diamond is 65% or greater, they are overweight and this characteristic can greatly vary. However, it should be remembered that a well-proportioned diamond as indicated by the total depth percentage may still have negatives in other aspects.
Every shape of diamond has different ranges for total depth percentage that is considered ideal. The following table gives the ranges that are generally considered best depth percentages for round brilliant cut diamonds. Fancies are also covered by the same guidelines, but emerald, radiant, and princess cuts are exceptions to this rule.
- Ideal = 58 – 60%
- Excellent = 60.1 – 62%
- Good = 62 – 64%
- Fair = 64 – 66%
- Poor = over 66% or under 57%
The table is the diamond’s largest cut facet. The facets are responsible for allowing light to enter and exit the gem. In determining proportions, one of the important factors is the size of the table facet. In addition to the depth percentage, a diamond’s table percentage is also important. The ratio of the table width with the total width is the table percentage. The bigger the table percentage in a round diamond, the bigger is the size of the diamond and the greater its brilliance.
The range of table percentage for diamonds is the following:
- Ideal = 53 – 58%
- Excellent = 58.1 – 60%
- Good = 60.1 – 64%
- Fair = 64 – 70%
- Poor = over 70%
The preference for table size varies in different parts of the world. However, a very small table range of 50% and below or a very large table range of 70% or more will negatively impact the diamond’s appearance, which in return will negatively impact the cut grade. Generally, today’s diamond cutters cut raw diamonds for an ideal to good table percentage between 55% – 65%.
The angles of a diamond are important but table percentage and depth percentage are equally important in determining the quality of the cut of a diamond and assessing its value.
This article was contributed by Frank Fisher.