Introduction
The table is the largest facet on a diamond — the flat, octagonal surface on top through which most light enters and exits. Its size relative to the diamond's overall width is called the table percentage, and it is one of the most influential proportions in determining how a round brilliant handles light.
Table percentage appears on every GIA grading report. It tells you how the cutter chose to balance brilliance against fire: a wider table favours brightness, a narrower table favours colour dispersion. This article covers what table percentage is, what the optimal range looks like, and what happens at the extremes. For the full set of round brilliant proportions, see Proportions Primer.
How Table Percentage Is Calculated
Table percentage is a ratio: the width of the table facet divided by the average girdle diameter, expressed as a percentage.
Table % = Table width / Average girdle diameter x 100
For example, a round brilliant with an average girdle diameter of 6.50 mm and a table width of 3.74 mm has a table percentage of approximately 57.5%.
GIA measures both values using precision instruments to the nearest hundredth of a millimetre. Because no round diamond is a perfect circle, the girdle diameter varies slightly — GIA uses the average of the minimum and maximum diameters. The reported table percentage reflects this averaged measurement, listed to one decimal place. For more on how diamond dimensions are taken, see Measurements in Millimetres.
The Optimal Range: 54-58%
For round brilliants, the optimal table percentage falls between 54% and 58%. Within this range, the table is large enough to admit substantial light into the stone while leaving sufficient crown facet area to produce fire.
Why this range works comes down to two competing roles. The table is the primary entry and exit point for light — a larger table admits more light and returns more brilliance (white light reflected back to the viewer). The crown facets surrounding the table act as dispersive prisms, separating exiting light into spectral colours — the flashes of red, blue, and green known as fire. Crown angle governs the dispersion angle; table percentage governs how much facet area is available for it.
The tension is straightforward: as the table grows wider, it claims area from the crown facets. More table means more brilliance but less fire. Less table means the opposite. The 54-58% range is where both qualities are well served. Most GIA Excellent-cut round brilliants fall within this window.
Values of 53% or 59% can still achieve Excellent when other proportions compensate — particularly when the crown angle and pavilion angle are optimally paired. But these sit at the edges of the optimal window, and moving further shifts the balance noticeably.
What Happens at the Extremes
Large tables: above 60%
When the table exceeds 60%, the crown facets become narrow strips with limited dispersive power. The diamond may appear bright, but the brightness has a flat quality — strong white light return without the colour flashes that give a well-cut diamond its visual complexity. Above 64%, the compressed crown height further degrades light exit geometry. Cut grades typically drop to Good or below.
A large table also reduces scintillation. Instead of a pattern of distinct, sharp reflections from multiple facets, the oversized table returns a single broad reflection — a flat mirror effect rather than dynamic sparkle. See What Cut Controls for more on how scintillation works.
Small tables: below 52%
When the table drops below 52%, the entry window for light shrinks. Even though the enlarged crown facets have more area for dispersion, there is less light to disperse. The stone may show flashes of colour in favourable lighting, but overall brightness is reduced.
Tables below 50% were characteristic of older cutting styles, including "old European" cuts from the early twentieth century — more fire-forward, less uniformly bright. GIA does not apply the current cut grade scale to these styles.
Table Percentage and Other Proportions
Table percentage does not operate in isolation. A 57% table with a 34.5° crown angle produces different light performance than a 57% table with a 32° crown angle. GIA's cut grading system evaluates proportions as an ensemble — the research behind the 2006 cut grade modelled millions of combinations, confirming that no single proportion determines quality on its own.
Use table percentage to understand a diamond's character, not to accept or reject it. A table at 55% within an Excellent-cut stone will lean toward fire. A table at 58% will lean toward brilliance. Both are valid — the question is which visual character you prefer. See Proportions Primer for how all five key proportions interact.
How to Read Table Percentage on a GIA Report
Table percentage appears in the proportions section of every GIA round brilliant report, alongside depth percentage, crown angle, pavilion angle, and girdle thickness. When comparing diamonds:
- Check the range. Does the table fall within 54-58%? Values of 53% or 59% are acceptable if the overall cut grade is Excellent.
- Read it with crown angle. A 58% table paired with a 34.5° crown angle is a strong combination. The same table with a 31° crown is not.
- Compare across candidates. Between two stones of similar weight and cut grade, the lower table percentage will tend toward more fire; the higher toward more brilliance.
For the full set of proportions and how to read them together, see Proportions Primer. For how cut grades translate to observable differences, see Cut Grade Scale.
Summary
Table percentage measures the width of the table facet relative to the diamond's diameter. For round brilliants, 54-58% balances brilliance and fire — a wide enough window for strong light entry and return, with enough crown facet area to produce spectral colour dispersion. Above 60%, fire diminishes and the stone appears flat despite being bright. Below 52%, insufficient light enters the stone, reducing overall performance.
The number appears on every GIA report and takes seconds to read. Use it not as a pass/fail criterion, but as a window into a diamond's visual character — whether it will favour clean white brilliance or the coloured flashes of fire. Paired with the other proportions on the report, table percentage helps you understand why a diamond looks the way it does, and whether that look is what you want.