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The tables below show the AGA Cut Grading system for round diamonds developed by D.
S. Atlas and his laboratory Accredited Gem Appraisers. This system has been adopted by the National
Association of Jewelry Appraisers (NAJA).
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CUT CLASSES
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Class1A
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Class1B
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Class 2A
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Class 2B
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American Ideal Cut
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International fine trade cut
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Table %
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53-58%
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52-60%
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51.5-63%
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51-64%
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Crown angle°
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34.0-34.7
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33-35.1
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32.1-35.8
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31.6-36.4
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Crown height %
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14-16.3%
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13.5-16.8%
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11.6-17.9%
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11.1-18.1%
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Pavilion Depth %
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42.8-43.2%
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42.5-43.5%
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42-44%
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41.5-44.9%
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Girdle Thickness:
Word descriptions
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Thin to Medium (1.0% to 3.0%)
Medium to Slightly thick (1.7% to 4.5%)
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Very thin to Slightly thick (0.4% to 4.5%)
Thin to Slightly thick (1.0% to 4.5%)
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Very thin to Slightly thick (0.4% to 4.5%)
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Very thin to Thick (0.4% to 5.5%)
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Total depth %
Determined by
factors already
considered above
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58-62.3%
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58.3-62.99%
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<58.3%
>63%
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Polish/Symmetry
NOT A PRIMARY
DETERMINING
FACTOR
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Excellent -Very Good
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Excellent toGood
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CUT CLASSES
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Class 3A
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Class 3B
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Class 4A
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Class 4B
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US domestic average cut
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below average
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Table %
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50.5-67%
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50-70%
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49-72%
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>72%
<49%
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Crown angle°
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30.1-37.9
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29.6-39.4
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29-40.5
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<29
>40.5
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Crown height %
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9.6-19.3%
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8.5-20.5%
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7.8-21.8%
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<7.8%
>21.8%
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Pavilion Depth %
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41-45.5%
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40.5-46%
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38-48%
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<38%
>48%
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Girdle Thickness:
Word descriptions
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Very thin to Very thick (0.4% to 7.0%)
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Extremely thin to Extremely thick (0.0% to >7.0%)
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Total depth %
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<58.3%
>63%
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Polish/Symmetry
NOT A PRIMARY
DETERMINING
FACTOR |
Good -Fair |
Poor
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A diamond called a "Tolkowsky Cut" is only approximated by cut
1A. However, a "Tolkowsky Cut" is a very specifically calculated cut with
the following parameters:
Table 53.0%, Crown Angle 34.6, Crown Height 16.2%,
Girdle Thickness app 1.7%, Pavilion Depth 43.1%. Many
diamonds are improperly called "Tolkowsky Cut" when they are only approximating
the parameters Tolkowsky formulated.
Courtesy of D.S. Atlas, Accredited Gem Appraisers, © AGA 1998-2004
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