The total depth percentage is a very important element of a diamonds proportions and it is greatly responsible for the amount of brilliance that a diamond will display.

Diamonds which have ideal to very fine cut with proper total depth percentage provide the greatest brilliance. The facets on the bottom of a round brilliant cut diamond are called pavilion facets. When you look at a round brilliant cut diamond face-up, the pavilion facets act as mirrors which reflect the image of the table, the large facet on the top of the diamond. This white table reflection seen within the center of the diamond provides the sparkle in the center of the diamond.

In a very fine to Ideal cut diamond the diamond will exhibit a white table reflection that appears in the center of the table. This reflection should be 1/4 to 1/2 the size of the large table facet on top of the diamond.

Total Depth Percentage = Depth Measurement / Average Diameter
Example: 60% = 6 millimeters / 10 millimeters = .60

Ideal to Very Fine Cut Diamonds have total depth percentages between 59% and 63%. Diamonds within this range usually provide excellent brilliance. Diamonds that have depths outside these ranges usually cost less, but a degree of brilliance is lost. The diagram below illustrates how the white table reflection changes in size as the depth percentage changes.

The white table reflection appears larger as the total depth percentage increases and smaller as depth percentage decreases.

• 55.0% = Girdle seen in table
• 56.0% = reflection broken up
• 57.0% = reflection broken up
• 58.0% = 1/8 size of table
• 59.0% = 1/4 size of table
• 60.0% = 1/3 size of table
• 61.5% = 1/3 size of table
• 62.5% = 1/2 size of table
• 63.5% = 5/8 size of table
• 65.0% = 7/8 size if table
• 66.0% = Dark table facets
• 67.0% = Dark star facets

When depth percentage becomes greater than 65% the center of the diamond becomes dark as light refracts through the bottom of the diamond.

The diagram displays the appearance of diamonds with total depth percentages that have proper crown height, crown angles, pavilion depth percentages and pavilion angles.

Proper Total Depth Percentage Does Not Guarantee Proper Cut. Total depth percentage is very important but it can sometimes be misleading. (See diagram below) Total depth percentage is a representation of a diamonds overall total depth. As the diagram illustrates, it is possible for two diamonds to have the same depth percentage and be proportioned differently.

Total depth percentage is a  combination of many other important elements of diamond cut. These elements include crown height, crown angle, pavilion depth percentage, pavilion angle and girdle thickness. These elements are  properly proportioned in ideal cut diamonds.

However, some diamonds with total depth percentages that are in the range of ideal may be improperly cut and display less brilliance.  A diamond with ideal  total depth percentage may also have an overly deep bottom, (deep pavilion depth percentage & steep pavilion angles) and have a very low top, (low crown height & shallow crown angle.) A simpler example would be two men that are six feet tall. One man has perfect symmetry. His upper body is in proper proportion to his lower body. The other man has very long legs and a short waist.

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