The Numbers Behind the Sparkle
When you look at a diamond grading report, you will see numbers for table percentage, depth percentage, crown angle, and pavilion angle. These proportions determine how light travels through the diamond and directly control how much the diamond sparkles. Understanding them helps you choose the most brilliant diamond possible.
Table Percentage
- What it is: The width of the flat top facet (the table) expressed as a percentage of the diamond's total width. A table of 57% means the flat top is 57% as wide as the diamond
- Ideal range (round brilliant): 54-57%
- Too small (<52%): Less light enters the diamond. Internal reflections increase but overall brilliance decreases
- Too large (>62%): The diamond becomes a window — light passes through instead of reflecting back. Reduced fire and sparkle
- Sweet spot: 55-57% is where most top-performing round brilliants fall
Depth Percentage
- What it is: The total height of the diamond from table to culet, expressed as a percentage of width. A depth of 61.5% means the diamond is 61.5% as tall as it is wide
- Ideal range (round brilliant): 59.5-62.5%
- Too shallow (<58%): Light leaks through the bottom (fish-eye effect). The diamond looks glassy and lifeless
- Too deep (>64%): Light leaks through the sides. The diamond looks dark in the center. The diamond also faces up smaller than its carat weight suggests
- Sweet spot: 61-62% for maximum brilliance
Crown Angle
- What it is: The angle of the crown facets (the angled facets between the table and the girdle) relative to the girdle plane
- Ideal range: 34-35 degrees
- Effect: Crown angle controls fire (the rainbow flashes). A steeper crown produces more fire but can reduce brilliance. A shallower crown produces more brilliance but less fire
Pavilion Angle
- What it is: The angle of the pavilion facets (the angled facets below the girdle) relative to the girdle plane
- Ideal range: 40.6-41.0 degrees
- Why it matters most: This is the single most critical proportion for sparkle. The pavilion angle determines whether light hitting the bottom facets reflects back up through the top or leaks out the side. Even a 0.5-degree deviation from ideal significantly reduces light return
How They Work Together
Diamond proportions are not independent — they interact. A shallower crown can compensate for a slightly steeper pavilion, and vice versa. The best diamonds have proportions that work in harmony, and the IGI or GIA cut grade evaluates this overall interaction. An Excellent cut grade means all proportions work together for maximum light performance.
