A diamond’s cut refers to its dimensions or proportions.  Cut also carries with it the idea of shape and style.  Some will argue that a diamond’s shape and cut are two different things, and they would be right, but for a time now some dealers have started to use one word to mean the other and vice versa.  So, this section will help you to recognize the different types of diamond shapes and cuts as well as how to tell if the cut is a good cut.

A diamond can be cut into many different styles and shapes such as Round, Pear, Radiant, Heart, Oval, Princess, and Marquise.  Some of these shapes and styles are self-explanatory as to their general appearance.  One of the most common diamonds for engagement rings would be the round diamond.

The dimensions to which the diamond is cut have a large impact on the diamond’s appearance and price.  The stone should be cut in such a way as to reflect as much light as possible back out of the top of the diamond.  If the pavilion, the bottom half of the diamond, is too shallow, the light may pass through the stone.  If there is too much depth, the light may exit out the side.  The first picture below illustrates an ideal cut, while the other two show poor cuts.

Before the dimensions for each type of diamond are give, several terms must be defined first.  Below is a figure that shows several critical parts and measurements of a diamond.  Depth and diameter are measurements and the rest are different parts of the diamond.

The most important formula used to maximize a diamond’s brilliance is the formula for depth percentage.  Other noteworthy metrics are table percentage and length/width ratio.


Few, if any, round diamonds are perfectly symmetrical.  The length/width ratio is determined by taking different diameter measurements on the diamond.  A perfect round diamond would have a 1:1 (1 to 1) ratio.  Other shapes will have other varying optimal ratios.  When looking for a diamond, its table and depth percentage will be found on its informational certificate.  Also on the certificate will be the diamond’s measurements.

        Example:  4.94-5.00 x 3.04

The first number is the smallest diameter measurement. The second number is the largest diameter.  The last number is the diamond’s depth.

Below is a table that gives values for a round diamond’s cuts.

  Ideal Excellent Very Good Good
Depth % 59% – 62.7% 58% – 63% 57% – 64.5% 56% – 65%
Table % 53% – 57% 53%-60% 53% – 62% 52.5%-66%


Other optimal shape specifications seem to be a bit inconsistent between sources.  Just remember, with any diamond you want the light to reflect back up at you in full brilliance.  You do not want to be stuck with a diamond that you can see through or a diamond that is dull and lifeless.

Finally, there is a couple of parts on the diamond yet to be mentioned: the girdle and the culet.  It is best to have a thin diamond girdle and a small to nonexistent culet.  The easiest way to determine these characteristics on a diamond is again by looking at its certification.