Depth & Table Percentage
Depth percentage is the depth of the diamond (measured from table to culet) divided by the diameter of the diamond. The higher the depth percentage number, the deeper or heavier the gemstone and therefore the less sparkle and brilliance it exudes. The lower the depth percentage number, the shallower or glassier the diamond appears, also resulting in less sparkle and brilliance. Mathematicians have established the theoretical "ideal" depth percentage for a diamond to return maximum light and offer maximum brilliance.
Table percentage is the length of the table facet divided by the diameter of the diamond. The higher the number, the bigger the table facet and the larger the surface area for leaking reflected light out of the diamond. The lower the number, the smaller the table dimensions and there is too little a surface area through which to see the internal brilliance of the diamond. As with the depth percentage, mathematicians have established the theoretical "ideal" table percentage for a diamond to offer maximum brilliance.
Laboratories have established general rules to rate the depth % and table %, and their effect on brilliance. Most laboratories now provide an overall "cut" grade which reflects the specific combination of depth %, table % and other factors, such as the following: