Gemological Institute Of America (GIA) Graduate Diamonds Practice Exam

The table percentage expresses how large the diamond’s table is relative to the stone’s overall width. The table is the flat facet on the very top, and its width is measured across the face, then divided by the diamond’s average girdle diameter and multiplied by 100 to give a percentage. Using the average girdle diameter, rather than a single girdle measurement, accounts for any slight asymmetry and gives a consistent reference across stones. This value tells you how big the top facet appears compared with the stone’s width, which influences light performance and appearance. So the correct concept is that the table size is expressed as a percentage of the average girdle diameter. The other ideas mix up what is being compared: it’s not the table depth, crown height, or a percentage of a single girdle dimension.