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About the GIA Facetware® Cut Estimator
Proportion Values and Ranges
Grading Considerations
Factors Affecting Results
GIA Facetware® Look-Up Tables



About the GIA Facetware® Cut Estimator

GIA Facetware® is a free online service that allows you to access GIA's database of more than 38.5 million diamond proportion sets in order to estimate the cut grade for any standard round brilliant diamond in the GIA D-to-Z color range and Flawless-to-I3 clarity range.

To predict a cut grade for a round brilliant cut diamond, GIA Facetware® requires the input of the following proportions: table size, crown angle, pavilion angle, star length, lower-half (lower-girdle facet) length, and average girdle thickness. Further limitations to the cut grade from girdle minimum and maximum, culet size, polish and symmetry grades, and painting or digging out can be explored. All parameters are given default values when the application is first opened. (back to top)

Click here for more information on the anatomy of a round brilliant diamond.



Proportion Values and Ranges

The GIA Diamond Cut Grading System and the GIA Facetware® Cut Estimator use averaged, rounded values for proportions when assessing diamond cut quality.

The rounding used by the system is as follows:

  • Total depth is rounded to the nearest multiple of 0.1%
  • Table size is rounded to the nearest multiple of 1%
  • Crown angle is rounded to the nearest multiple of 0.5°
  • Pavilion angle is rounded to the nearest multiple of 0.2°
    • Pavilion angles ending in odd numbers are always rounded UP, for example 40.7° would be rounded to 40.8°
  • Star length is rounded to the nearest multiple of 5%
  • Lower-half (lower-girdle facet) length is rounded to the nearest multiple of 5%

Measurement precision and rounding was determined by considering:

  1. The precision of measuring devices and other measuring methodologies
  2. The practical abilities of most diamond cutters and manufacturers
  3. The differences in cut quality that were found to be consistently distinguishable during our extensive observation testing

These three considerations work together, so we used the highest level of precision that could be applied in all three categories. 

Proportion ranges shown in GIA Facetware® represent those most typically seen in the trade. Predicted cut grades for diamonds with proportions or parameters outside these ranges are not available; in most cases these diamonds would receive the lowest cut grade in the system. (back to top)


Grading Considerations

Although GIA Facetware® provides estimated cut grades based on all of the proportions and finish assessments of a standard round brilliant diamond, there are three main areas of grading that can be considered before using GIA Facetware® to estimate the potential cut grade. The tables below provide the highest possible GIA Cut Grade that can be achieved for various assessments of Girdle Thickness, Culet Size, and Finish (Polish and Symmetry); these are all quality elements of a diamond that are visually assessed by graders at the GIA Laboratory.  As an example, to qualify for an Excellent cut grade in the GIA Diamond Cut Grading System, a diamond’s girdle thickness needs to be between Thin (THN) and Slightly Thick (STK). (back to top)

 

 

 

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Factors Affecting Results

The GIA Facetware® Cut Estimator is intended to provide an estimation of the cut grade that would be received from the GIA Laboratory for the same diamond. However, there are several reasons why the grade provided by GIA Facetware® may be different from that received from the GIA Laboratory. Some of the reasons are:

  • The diamond's actual proportions (such as the crown angle or star length) or visually assessed parameters (such as the girdle thickness or symmetry) as determined by the GIA Laboratory are different from the proportions or parameters assumed by the user.

  • The diamond has been manufactured using non-standard brillianteering such that it is significantly "painted" or "dug-out" (i.e., the diamond has its upper- and/or lower-half facets fashioned at tilt angles different from those traditionally used for standard round brilliant diamonds). Click here to learn more.

  • The accuracy and tolerances of different methodologies and optical devices used to measure a diamond's proportions or parameters may differ from those used by GIA. Click here to learn more.

To learn about other important limitations of the software or limitations on use of the software for business purposes, please familiarize yourself with the Assumptions and Terms of Use, available through the software interface. (back to top)

To begin using the GIA Facetware® Cut Estimator, please click below:




GIA Facetware® Look-Up Tables

You can now view the cut grade results from the GIA Facetware Database in table format, which allows you to visualize how cut grades change through proportion space. This format may be especially helpful to manufacturers who would like to know how to change proportion values to attain better GIA cut grades.

Currently, the tables allow you to vary only the table size, crown angle and pavilion angle only. By choosing a value for one of these proportions from one of the pull-down menus, you will be directed to the appropriate cut grade look-up table in which your chosen value is the constant, and differences in the other two proportions are shown in the x- and y-axis.

To access GIA Facetware Look-up Tables, please click on one of the following links:

Table %
Pavilion Angle
Crown Angle

Please Note: The estimated cut grades represented in these tables apply ONLY to standard round brilliant diamonds in the D-to-Z color range. The estimated cut grades shown in these tables assume default values for other proportions and finish, and may not be correct for diamonds with different values for these default parameters. The default values for these other parameters are as follows:

Star Length = 55%
Lower-Half Length = 80%
Polish and/or Symmetry = VG or EX
Girdle Thickness = 3.0%
Girdle Min/Max = THN-STK
Culet Size = NON-SML

In addition, estimated cut grades shown may not be correct if your diamond is "painted" or "dug out." For a description of these manufacturing methods please see our article here [PDF].

Please read the Assumptions and Terms of Use for more information regarding the use of the GIA Facetware Look-Up Tables. (back to top)