Complete Instructions for the American Gem Society Laboratories
Proportion Based Cut Grading System for the Standard Round Brilliant
Polish and Symmetry
The Ideal Cut Grade can have Ideal or Excellent polish and symmetry
An Excellent Cut Grade can have Ideal or Excellent or Very Good polish and symmetry
Essentially, polish and symmetry grades can be one grade lower than the assigned cut grade
Table Diameter Sizes
52 to 65%
Girdle Thickness
The Ideal Cut Grade can have girdle thicknesses of Thin, Medium or Slightly Thick at the ‘valleys’ or ‘scallops’.
Highest grade achievable with up to a 4.5% girdle, at any point, is Ideal
Highest grade achievable with >4.5 to 5.5% girdle, at any point, is Excellent
Highest grade achievable with >5.5 to 6.5% girdle, at any point, is Very Good
Highest grade achievable with >6.5 to 7.5% girdle, at any point, is Good
Highest grade achievable with >7.5 to 10.0% girdle, at any point, is Fair
Highest grade achievable with >10.0% girdle, at any point, is Poor
Extremely thin or very thin girdle, at any point, reduces the cut grade by one grade
Weight Ratio
This is factored into the Proportion Charts
Star Length
All inclusive from 45 to 55%
Lower Girdle Length
All inclusive from 75 to 85%
Painting and Digging
Maximum digging of the upper half facets is 3 degrees of azimuth
Maximum painting of the upper half facets is 4 degrees of azimuth
Maximum digging of the lower half facets is 3 degrees of azimuth
Maximum painting of the lower half facets is 3 degrees of azimuth
Rounding
Table diameter percentage is rounded to the nearest 1%. 55.4% = 55%. 55.5% = 56%.
Pavilion angle is rounded to the nearest tenth of a degree. 40.74° = 40.7°. 40.75° = 40.8°
Crown angle is rounded to the nearest half degree. 34.24° = 34°. 34.25° = 34.5°
Note: All angles and percentages on AGSL documents are reported to the accuracy of the Sarin DiaMension measuring device, but the
above rounding is used for calculating the proportion cut grade.
Culet Size
Highest grade achievable with none, very small, small or medium is Ideal
Highest grade achievable with slightly large is Very Good
Highest grade achievable with large is Good
Highest grade achievable with very large or extremely large is Fair
Any standard round brilliant cut outside of any of the above parameters must be cut-graded using
the patented AGS Performance Grading Software
Copyright 2008 American Gem Society Laboratories