Round Brilliant Cut Diamonds Assessment Guide Chart In-Depth Information

Round Brilliant Cut Diamonds Assessment Guide Chart In-Depth Information

Round Brilliant Cut Diamonds Assessment Guide Chart In-Depth Information

Posted by Sear R. on 7th Jul 2018

excellent round cut diamond

Round Brilliant Cut Diamonds make up roughly 70-80% of all polished diamonds traded around the world. Due to progress in research and the development of a standard method for grading diamonds, round diamonds have become more like a commodity, and its prices are increasingly becoming standard with very small margins for markups by retailers.  

The Gemological Institute of America (GIA) Introduced the standard cut grading system for "unmodified" round brilliant cut diamonds in 2005. According GIA, for a round diamond to qualify as an unmodified round brilliant cut diamond, it has to have 58 facets and cut according to modern standards. American Gems Society (AGS) on the other hand uses a proportions-based grading system. 

In terms of cut, while many marketers call their round cut diamonds with taglines like "heart & arrows", "hearts on fire", "a cut above" etc., the benchmarks and method for cutting a round brilliant cut diamond is more or less the same, and as long as you follow the guidelines below, you should be able to determine what a well-cut round diamond is regardless of its brand name! 

Analyzing the Cut:

The following benchmarks can serve as a helpful guide while evaluating the cut of a round brilliant cut diamond

Depth %
  • Poor/Fair: <56/>65%
  • Good: 57.6-58/63-64
  • Very Good: 58-59/62-63
  • Excellent: 59-62
  • Table %
  • Poor/Fair:<50/>68.5>
  • Good:51-52/61-64
  • Very Good: 51-53/59-60
  • Excellent:58-53
  • Culet
  • Poor/Fair: Medium
  • Good: Small
  • Very Good: None/Very Small
  • Excellent: None
  • Crown Angle
  • Poor/Fair:<28.5/>38.5
  • Good: 30-32/36-38
  • Very Good: 32-34/35-36
  • Excellent: 34-35
  • Pavilion Depth
  • Poor/Fair: <39/>46
  • Good: 41-42/44-45.3
  • Very Good: 42-42.6/43.3-43.8
  • Excellent: 40.5-41.5
  • Girdle
  • Poor/Fair: Ex. Thin – Ex. Thick
  • Good: Very thin - thick
  • Very Good: Very thin - slightly thick
  • Excellent: Thin - slightly thick
  • In Depth Video Explanation on How to Analyze the cut of a Round Cut Diamond:

    How to compare and compromise on round cut diamonds?

    One of the hardest questions or shoppers often is how to compare round diamonds and what C of the 4Cs should they compromise on - Carat Weight, Cut, Clarity, and Color. Please watch the video below where we explain four scenario which would help you in deciding what approach is best for you within your budget:

    Suggested carat weight, cut, color and clarity of Round Brilliant Cut Diamond for people with budget constraints:

    Excellent Choice:

    • At least 1.0 carats in Weight
    • Very Good or Excellent Cut with Very Good to Excellent Polish and Symmetry
    • G or above in color
    • SI1 or above in clarity
    • No Florescence

    Very Good Choice:

    • At least 0.90 carats in Weight
    • Good or Very Good Cut with Good to Excellent Polish and Symmetry
    • H or above in Color
    • SI2 or above in Clarity
    • No Florescence

    Good Choice:

    • At least 0.80 Carats in Weight
    • Good Cut with Good to Very Good Polish and Symmetry
    • I or above in Color
    • SI2 or above in Clarity
    • None, faint or medium blue florescence


    In today’s marketplace, roughly 75% of all diamonds sold are round shaped. There are varieties of round cut diamonds available, but the most common ones have 57 to 58 facets. Since 1750, diamonds have witnessed a plethora of changes especially in variation of facet size and proportions. New styles and changes are made especially in the diamond’s table size, total depth, culet size, crown height, and length of the lower half facets.

    Nonetheless, diamonds from every era have had unique and quite discrete appearances. Some of the conspicuous changes in diamonds include larger table facets, smaller culets, and longer lower half facets.

    Most consumers tend to choose round brilliant cut diamonds because it meets their modern concepts of aesthetics. Round brilliant cut diamonds have tighter mosaic of light and dark patterns with longer lower half facets which gemologists categorize as “splintery” pattern.

    The older cuts like the old European cut have small table, large culet, steep crown, and shorter lower half facets, which gives them a “blocky” or “checkerboard” pattern. In spite of their beauty, it is quite difficult to judge them against modern round brilliant cut diamonds due to differences in their propo rtions

    The Gemological Institute of America introduced the cut grading system for unmodified round brilliant cut diamonds. In order to distinguish between the older style brilliant cut diamonds, the term “unmodified round brilliant” is used for a symmetrical round cut diamond which has 58 facets and is cut according to the modern standards. 

    GIA uses five cut grades including Excellent, Very Good, Good, Fair, and Poor to determine the cut of a round cut diamond. AGS on the hand uses six cut grades by adding "ideal cut" to the equilibrium.

    Here are some of the key differences between old european and modern round brilliant cut diamonds:

    According to GIA, old European cuts have the following specifications:

    1. Lower half facet length: less than or equal to 60 percent
    2. Table size: less than or equal to 53 percent
    3. Crown angle: greater than or equal to 40 percent
    4. Culet size: slightly large or larger

    While the 58—facet round brilliant cuts have to meet the following requirements to be called modern brilliant cuts:

    1. Lower half length: less than or equal to 60 percent
    2. Culet size: medium or larger
    3. Star length: less than or equal to 60 percent.


    The image above is a good side by side comparison of the two different round diamond cuts. Notice the European cut has a small table, large culet, and short lower-half facets, while the round brilliant cut has larger table, smaller culet, and a much longer lower-half facets.

    Here an illustration of an AGS Ideal Round Brilliant Cut Diamond:

    Ideal Cut Diamond

    Evaluating Round Brilliant Cut Diamonds