The Numbers Behind the Sparkle
When you look at a diamond grading report, two percentages determine more about your diamond's beauty than almost anything else: depth percentage and table percentage. These two numbers control how light moves through the diamond — and whether it comes back to your eyes as brilliant sparkle or leaks out the bottom as wasted light.
What Is Table Percentage
- Definition: The table is the flat top facet of a diamond — the largest facet, the window you look through. Table percentage is the width of that flat top divided by the total width of the diamond
- Ideal range for round brilliant: 54-57% is considered optimal by most gemological laboratories. This range maximizes the balance between brilliance (white light return) and fire (rainbow flashes)
- Too large (above 62%): The diamond becomes a window — light passes straight through without being reflected back. You see through the diamond instead of seeing sparkle
- Too small (below 52%): Light gets trapped bouncing between the crown facets too many times and loses energy. The diamond can appear dark in the center
What Is Depth Percentage
- Definition: The total height of the diamond (from table to culet) divided by the total width. This tells you how deep the diamond sits relative to its spread
- Ideal range for round brilliant: 59-62.5% balances light performance with visual size
- Too deep (above 64%): Light leaks out the bottom. The diamond carries weight in depth rather than spread — a 1.00 ct deep diamond looks smaller than a 1.00 ct well-proportioned diamond
- Too shallow (below 57%): Light leaks out the pavilion. The diamond may look larger face-up but will lack brilliance and fire. A classic case of trading sparkle for size
How They Work Together
- Balanced proportions: A diamond with 56% table and 61% depth creates a harmonious light path. Light enters the table, bounces off the pavilion facets at the correct angle, and exits back through the crown as brilliance and fire
- Imbalanced proportions: A diamond with 65% table and 55% depth (spread-stone) prioritizes face-up size over light performance. It looks bigger but sparkles less
- The trade-off: You can have a diamond that looks big OR one that sparkles intensely. The best diamonds balance both, which is why the ideal ranges exist
Practical Buying Advice
- Always check table and depth percentages on the grading report before purchasing
- For round brilliant: look for 54-58% table and 59-62.5% depth
- For fancy shapes, ideal ranges differ — but the principle is the same
- Two diamonds with the same carat weight can look dramatically different sizes depending on their depth percentage
- An Excellent cut grade from IGI or GIA already accounts for these proportions — but double-checking gives you extra confidence