Girdle thickness is somewhat of a judgement call. If a girdle is Medium to Thick, then this could mean 1/3 of it is Medium, 1/3 is Slightly Thick, and the remaining 1/3 is Thick. The term “Medium to Thick” may have several meanings. It may be that 85% of the diamond’s girdle is medium, whereas the remaining 15% is thick. In such a case, the entire adjustment percentage cannot be added into the formula. A stone with a more consistently thick girdle will require you to add a larger adjustment percentage to the formula.
Thin: less than 0.15 millimeters
Medium: between 0.15 and 0.20 millimeters
Slightly Thick: between 0.20 and 0.23 millimeters
Thick: between 0.23 and 0.33 millimeters
Very Thick: between 0.33 and 0.40 millimeters
Extremely Thick: grater than 0.40 millimeters
These measurments might be difficult to take for the thickness, but it will give you an idea of what to look for. The measurments are consistent regardless of the stone size. Courtesy of Adamas Gemological Laboratory.
| Girdle Thickness Range=Girdle Thickness Average | Girdle Thickness Adjustment | ||
| “-” represents slightly thinner “+”represents slightly thicker |
3.1mm-4.1mm | 4.15mm-6.90mm | 7.00mm+ |
| Extremely Thin | 0.97 | 0.96 | 0.95 |
| Extremely Thin to Thin = Thin – | 0.98 | 0.97 | 0.965 |
| Extremely Thin to Medium = Thin | 0.985 | 0.98 | 0.975 |
| Extremely Thin to Slightly Thick = Medium – | 0.99 | 0.985 | 0.98 |
| Extremely Thin to Thick = Slightly Thick – | 1.025 | 1.015 | 1.005 |
| Extremely Thin to Very Thick = Thick | 1.04 | 1.03 | 1.02 |
| Extremely Thin to Extremely Thick = Thick + | 1.045 | 1.035 | 1.025 |
| Thin | 0.985 | 0.98 | 0.975 |
| Thin to Medium = Medium – | 0.99 | 0.985 | 0.98 |
| Thin to Slightly Thick = Medium | NA | NA | NA |
| Thin to Thick = Slightly Thick | 1.03 | 1.02 | 1.01 |
| Thin to Very Thick = Thick – | 1.035 | 1.025 | 1.015 |
| Thin to Extremely Thick = Very Thick – | 1.07 | 1.05 | 1.035 |
| Medium | NA | NA | NA |
| Medium to Slightly Thick = Medium + | 1.015 | 1.01 | 1.05 |
| Medium to Thick = Slightly Thick | 1.03 | 1.02 | 1.01 |
| Medium to Very Thick = Thick – | 1.035 | 1.025 | 1.015 |
| Medium to Extremely Thick = Thick + | 1.045 | 1.035 | 1.025 |
| Slightly Thick | 1.03 | 1.02 | 1.01 |
| Slightly Thick to Thick = Thick – | 1.035 | 1.025 | 1.015 |
| Slightly Thick to Very Thick = Thick | 1.04 | 1.03 | 1.02 |
| Slightly Thick to Extremely Thick = Thick + | 1.045 | 1.035 | 1.025 |
| Thick | 1.04 | 1.03 | 1.02 |
| Thick to Very Thick = Very Thick – | 1.07 | 1.05 | 1.035 |
| Thick to Extremely Thick = Extremely Thick – | 1.09 | 1.075 | 1.05 |
| Very Thick | 1.09 | 1.065 | 1.045 |
| Very Thick to Extremely Thick = Ex. Thick – | 1.09 | 1.075 | 1.05 |
| Extremely Thick | 1.11 | 1.08 | 1.06 |
| The above table of girdle thickness adjustment multipliers (GTA) will be used shortly in weight estimation formulas. Please refer back to this table when studying estimation examples. | |||
A very thin to thick girdle. Some parts are medium so the average would be slightly thick.