Table percentage

Table percentage is the width of the table facet — the flat top facet of a faceted diamond — expressed as a percentage of the stone's average girdle diameter. On every GIA Diamond Grading Report the number sits in the proportion summary under the crown angle. The GIA Excellent cut grade window for round brilliants runs 53% to 58%; the AGS Ideal-0 band is tighter at 53% to 57%. Above 60% a round usually drops to Very Good; above 64% it drops to Good regardless of how clean the other proportions look.

Table percentage trades fire for spread. Larger tables (60% and up) face up larger for the same carat weight because the flat top facet covers more of the visible crown — a 1.05 ct round with a 62% table can read like a 1.10 ct face-up. The cost is fire: a wide table refracts less of the incoming light into its spectral components, returning more white brilliance and fewer rainbow flashes. Smaller tables (53% to 55%) return more fire because more of the incoming light hits the bezel facets at the steeper crown angle and disperses on the way back out. The trade-off is spread — a 1.00 ct round with a 53% table can face up like a 0.97 ct.

The intersection between table % and crown angle determines what the stone actually does. A steep crown (35°+) with a small table (54%) produces a fire-dominant round in the Tolkowsky tradition. A shallow crown (33°) with a large table (60%) produces a spread-dominant modern commercial cut common in mass-market rounds. AGS Light Performance grading penalises both extremes; GIA Excellent admits both as long as the proportions fall inside the published bands.

Star length is the second-order proportion that interacts with table percentage. A round with a 56% table and 50% star length (the AGS Tolkowsky-anchored reference) looks materially different from a 56% table / 60% star round even though both can earn GIA Excellent. The star length tunes the scintillation pattern near the center of the stone; the table % sets the spread/fire ratio.

For a buyer comparing two GIA Excellent rounds with similar everything else, table percentage is the proportion that explains why one stone looks fiery and the other looks bright but flat. 55% to 57% is the practical sweet spot for a round being judged on light performance rather than face-up size.