How Much Does Diamond Depth and Table Percentage Matter?
They matter significantly — depth and table percentage are two of the most important proportion measurements that determine how a diamond handles light and how large it appears for its carat weight. They are key inputs to the cut grade, and understanding them helps you evaluate diamonds beyond the grade label.
What These Measurements Mean
Total depth percentage is the height of the diamond from table to culet, expressed as a percentage of the diamond's average diameter (for rounds) or width (for fancy shapes). A round brilliant with a 6.50 mm diameter and a total depth of 3.90 mm has a depth percentage of 60.0%.
Table percentage is the width of the table facet (the large flat facet on top) expressed as a percentage of the diamond's average diameter. A round brilliant with a 6.50 mm diameter and a 3.64 mm table has a table percentage of 56%.
Both measurements appear on the grading report and are readily available for comparison.
Why Depth Matters
Depth percentage directly controls two things:
1. Light return. The combination of crown height (above the girdle) and pavilion depth (below the girdle) determines the angle at which light bounces between the pavilion facets. When the pavilion is too deep, light exits through the side of the diamond instead of reflecting back up through the crown. When the pavilion is too shallow, light passes straight through the bottom. In either case, the diamond loses brightness.
2. Face-up size. A deeper diamond carries more of its weight below the girdle, where it is invisible from above. Two 1.00 ct round brilliants — one with 59% depth and another with 64% depth — can differ by 0.3–0.4 mm in diameter. That is a visible difference, and it means the deeper stone looks smaller despite weighing the same.
For round brilliants, the ideal total depth range is approximately 59.0–62.5%. Diamonds within this range typically deliver good light performance and efficient weight distribution.
Why Table Matters
The table facet is the primary window for light entering and exiting the diamond. Its size relative to the diameter affects the balance between brilliance and fire:
- A larger table (above 60%) allows more white light to exit directly, emphasising brilliance. But it reduces the crown area, which limits the facets that produce fire (spectral dispersion).
- A smaller table (below 53%) increases the crown's relative area, which can produce more fire. But if too small, the diamond may appear dark or show reduced overall brightness.
For round brilliants, the ideal table range is approximately 54–58%. This range delivers a balanced combination of brilliance and fire. Tables between 58% and 60% are acceptable but tend to favour brightness over fire.
How Depth and Table Interact
These proportions do not work in isolation. They interact with crown angle, pavilion angle, girdle thickness, and other parameters to create the diamond's overall optical performance. For example:
- A 60% depth with a 56% table and a 34.5° crown angle / 40.8° pavilion angle is a classic well-performing combination.
- A 62% depth might still perform well if the extra depth comes from a slightly thicker girdle (which does not harm light return significantly) rather than from a steeper pavilion.
GIA's cut grading system evaluates these interactions holistically, which is why the cut grade is generally a more reliable single indicator than any individual proportion. But understanding depth and table helps you identify why a diamond performs the way it does.
Depth and Table in Fancy Shapes
Fancy shapes lack standardised cut grades, making proportion analysis more important:
- Ovals and cushions: depth percentages of 58–65% are typical. Deeper stones may show pronounced dark areas (bow-tie effect) and reduced face-up size.
- Emerald cuts: depth percentages of 60–67% are common. Table percentages are typically larger (60–70%) because the step-cut design uses broad, open facets.
- Each fancy shape has its own proportion guidelines, and the acceptable ranges are wider than for round brilliants.
Practical Application
When comparing diamonds, check depth and table percentage alongside the cut grade:
- Prefer depths of 59–62.5% for round brilliants. Below 58% risks being too shallow; above 63% risks being too deep.
- Prefer tables of 54–58% for round brilliants. This range balances brilliance and fire.
- Compare face-up dimensions (millimetres), not just carat weight. Depth percentage tells you whether the diamond is efficiently spread or hiding weight below the girdle.
- Use HD video to confirm. Proportions on paper predict performance; video shows it. At Arete Diamond, every stone includes video so you can see how depth and table translate into real light performance.
When to Care More vs Less
If you are buying a round brilliant with a GIA Excellent cut grade, depth and table are already within a good range — the cut grade confirms this. Proportion analysis becomes more valuable when:
- Evaluating fancy shapes (no standardised cut grade)
- Comparing two diamonds with the same cut grade (fine-tuning within Excellent)
- Assessing diamonds from labs that do not provide a cut grade
Learn More
- Table Percentage — how table size affects light behaviour
- Total Depth Percentage — depth and its impact on performance and size
- Proportions Primer — how all proportions interact
- Diamond Anatomy — crown, pavilion, girdle, table, and culet explained