The girdle is the outer edge of a diamond. The grade of diamonds girdle is determined by the appearance of the girdle at its thinnest point and thickest point. A diamond's girdle can be faceted, polished smooth, or have a slightly granular appearance. Very fine cut diamonds often have faceted girdles. A diamond cutter must spend extra time to carefully facet a girdles edge. A faceted girdle does not improve a diamonds grade. GIA grades only thickness of a diamonds girdle and not the surface appearance.

Ideal girdle thickness should range between Very Thin to Thick. Sometimes a diamond can have a perfect medium girdle around ninety-nine percent of its diameter and is only very thick at one very minute isolated point. This diamond will receive a GIA girdle grade as medium to very thick. In this case, choosing a diamond with a very thick girdle could be acceptable because only one minute part of the girdle reached very thick and it will unlikely affect the diamonds appearance. This judgment can only be made by visual inspection by a trained Certified-Gemologist-Appraiser. Diamonds that have grades extremely thin, very thick, or extremely thick are usually not recommended.

Abbreviations For Girdle thickness:

EXTN, ET, XT, EXN = Extremely Thin
VTN, VT, VETN = Very Thin
T, TN, TH = Thin
M, ME, MD = Medium
STK, ST, SLTK, SLTH = Slightly Thick
T, TK, TH = Thick
VTK, VTH, VETK, VET = Very Thick
ET, EXTK, XT, XTK = Extremely Thick
F, FA, FAC = Faceted
S, SM = Smooth
P, PO = Polished