Round Brilliant Diamond

About the round brilliant cut

The round brilliant is the most researched diamond shape available of all engagement ring cuts. Cutters have been using precise mathematical calculations and advanced theories of light behaviour for many years. This has optimized the fire and brilliance in a round diamond.

It was in 1919 when the round shape started to become more popular after Marcel Tolkowsky published ‘Diamond Design: A Study of the Reflection and Refraction of Light in Diamond’. His work described the ideal proportions of a round cut diamond to maximise its brilliance and fire. His thesis has since been worked on by diamond manufacturers to further improve a round diamond cut.

A round diamond gives more flexibility than other engagement ring cuts in terms of balancing cut, colour and clarity grades while still generating the fire and brilliance of the stone. Most round diamonds are brilliant cut which means they have 58 facets, or 57 when there is no culet (the small area at the bottom of the diamond’s pavilion).

Colour and Clarity

Evaluating the colour and clarity of round cut diamonds is based on personal taste. For example, GIA classification states that a diamond of more than 50 carats is rated as ‘excellent’ with the colour grading of D-F and ‘very good’ at H-I. Yet some people may actually prefer a G-H colour graded diamond which has a mixture of warmer colours than an ‘excellent’ D-F which is cooler and colourless.

Likewise, preference for the clarity of the diamond is unique to personal taste. Some people don’t mind inclusions as long as they cannot easily see them, while others prefer a flawless appearance.


Round diamonds are more expensive than fancy diamond shapes on a carat per carat basis. This is, firstly, because the demand for round diamonds is high, while the yield is low. And, secondly, because more of the diamond is lost in the cutting process of the round brilliant than in other engagement ring cuts. Even with modern techniques, cutting and polishing a diamond crystal usually results in a dramatic loss of weight. (It normally loses 50% of its weight.) It is likely that a typical round cut diamond will cost 25-35% more than a fancy cut diamond.

Advice when opting for a round brilliant cut diamond

It is generally recommended to opt for one of the two highest cut grades of the traditional round diamond so that the diamond’s brilliance is maximised. The two highest cut grades are ‘ideal’ and ‘very good’. In addition, ‘ideal’, ‘excellent’ or ‘very good’ polish and symmetry grades are preferred for this cut. cut.