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We all know that a diamond's cut grade is important, but it is also important to understand what separates a diamond with an “Ideal” cut grade from a diamond that is actually ideally cut. Just because a diamond has an ideal cut grade does not always mean that it will make the cut when we are selecting a diamond for our clients as we are extremely particular about the quality of diamonds that leaves our shop. There are several factors to take into consideration when examining a diamond ideal proportions, as well as how these factors interact with one another. If you have any questions or would like to find out more, please feel free to get in touch with our consultants, and we will be glad to assist you.

The anatomy of any diamond consists of the Table, Crown, Girdle, Pavilion and Culet. The proportions and angles of these components affect how light is refracted and reflected which directly affects how optimal a diamond’s sparkle is.

Table Percentage:

As there is currently no internationally accepted standard for grading the cut of fancy cut diamond shapes, you will not find such criteria on your fancy shaped diamond certificate. There is much controversy behind what constitutes an ideal proportion for fancy cut diamonds, and there are other subjective factors to consider such as how one might prefer a rounder oval, or a longer radiant. However, we shall still compile a table of ideal proportions for all the diamond shapes for you to use as a reference.

Contrary to popular belief, bigger is not always better when it comes to the Table Percentage. Having a table percentage that is too small, or even too large, will compromise how brilliant the diamond looks. This is calculated by having the size of the table, divided by the diameter of the diamond as a percentage. There are many differing ranges of percentages online for what constitutes an ideal table percentage. But a table percentage somewhere in the range of 54-57% for a round diamond cut grade would be considered ideal. We try as much as possible to select a diamond with a larger table within this range, ideally between 56-57%. We might even consider 57-58% on occasions when every other aspect of the diamond’s proportions line up well to create an ideally cut diamond.

Depth Percentage:

The Depth Percentage is equally as important when it comes to how good your diamond looks. It is calculated by having the depth of the diamond (distance between the table and culet), divided by the diameter of the diamond as a percentage. If the depth is either too shallow, or too deep, it results in the light not being able to reflect off the pavilion and back out the table. The light leaks out through the bottom of the diamond, creating a dark or dull appearance. An ideal depth percentage would be in the range of 60 - 62.5%.

Crown and Pavilion Angles:

Crown and Pavilion angles are measured using the Girdle as the reference line. These two angles are also important in ensuring a sparkly diamond, and are usually correlated with the Table and Depth Percentages. If the angles are too small, this is usually indicative of a shallow depth percentage, which causes the diamond to appear glassy, and vice versa.

Ideal crown and pavilion angles are in the range of 33.7 - 35.8% and 40 - 42% respectively.


This aspect of a diamond does not often play a significant role in choosing your diamond. A thin - slightly thick Girdle would be characteristic of an ideal diamond. However, a diamond with an extremely thick girdle does not necessarily lack sparkle, but rather that too much weight would be concentrated around the centre of the diamond, making the diamond look smaller than other diamonds of a similar carat weight. On the other hand, an extremely thin girdle poses a higher risk of chipping along the edge during the setting process, or when being worn.


Pronounced “kyü-lət”, the Culet refers to the bottom tip of the diamond. The ideal grading of a culet is “None” which is also the same as “Pointed”. This means that there is no facet at the bottom tip of the diamond, hence why it is pointed. As opposed to having a flat facet which is parallel to the table.

Traditionally, a culet facet was included to protect the diamond’s tip from chipping as a pointed culet can be fragile. However, it is an additional facet to allow light to escape from the bottom of the diamond which is undesirable, so a pointed culet possesses the best light qualities.

Other factors that affect the grade of a diamond apart from the cut include the Polish, Symmetry, and Fluorescence. Click here to read more about it!

We hope that you now have a better understanding of how the proportions of a diamond affect its grade, and more importantly, its appearance. It is also important to understand how these theories translate to how we perceive a diamond’s appearance in person. Very often as consumers, we get too caught up in the technical aspects of choosing a diamond, and forget that a diamond is meant to be appreciated with the naked eye.