Round Brilliant Cut Diamonds Assessment Guide Chart In-Depth Information - Petra Gems

Round Brilliant Cut Diamonds Assessment Guide Chart In-Depth Information

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excellent round cut diamond

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. AGS on the other hand uses a proportions-based grading system. 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: 42.8-43.1
  • Girdle
  • Poor/Fair: Ex. Thin – Ex. Thick
  • Good: Very thin - thick
  • Very Good: Very thin - slightly thick
  • Excellent: Thin - slightly thick
  • 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 proportions. 

    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

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