Diamonds 101: What’s a Diamond Girdle?

The girdle is a diamond’s outermost edge, where the top of the diamond (crown) meets the bottom of the stone (pavilion). When you look at a polished diamond in its setting or from a profile view, the girdle is the widest part of the stone – just look for the portion of the stone that makes contact with the setting itself.

It is important to remember that girdle is measured as a percentage of the diameter, and its descriptions are relative to the size of the stone. This means that a measured thickness of 0.31mm may result in a “Very Thick” rating for a 1/2-carat round diamond, while thickness of 0.31mm will result in a “Thin-Medium” rating on a 5-carat diamond.

Grading reports also include the finish of the girdle, although they have no impact on the appearance or value of the diamond – polished (a bruted girdle that has been polished smooth), faceted (a series of tiny polished sides going around the diamond), or bruted (the less common of the three, meaning a single continuous unpolished surface).

3 Ways in Which a Girdle Impacts a Diamond

There are three major ways in which a diamond’s girdle can affect the stone:

• The thickness of the girdle affects the relative position of the surrounding facets, so it can impact the cut of a diamond. Take into account that girdle width is already factored into the diamond's overall cut grade, so if you own a well cut diamond it already produces produce superior brilliance, fire, and scintillation - even if the girdle itself is not in the ideal Thin-Slightly Thick range of width. The extreme girdle variations (very thin – extremely thick) may indicate poor cut. Extreme variations can also cause problems during the setting process.
• A thicker girdle will add weight to a diamond, thereby increasing its price - though minimally.
• An "Extremely Thin" girdle is more susceptible to chipping.

Girdle Classifications

Girdle thickness and finish are classified into categories ranging from extremely thin to extremely thick, and are usually abbreviated thus:  

• Extremely Thin – ETN, ETH, XTN, EXN.
• Very Thin – VTN, VT, VETN
• Thin – T, TN, TH
• Medium – M, ME, MD, MED
• Slightly Thick – STK, ST, SLTK, SLTH
• Thick – T, TK, TH
• Very Thick – VTK, VTH
• Extremely Thick – ET, EXTK, XT, XTK
• Faceted – F, FA, FAC
• Smooth – S, SM

 If you’re seeking ideal cut diamonds, look for a stone with a girdle rated somewhere between “Thin” and “Thick”.