Ideal proportions for a Round Brilliant Cut Diamond

The round brilliant cut diamond is the most popular diamond shape, and its proportions are critical to its overall appearance, particularly its brilliance, fire, and scintillation. The most commonly agreed-upon ideal proportions for a round brilliant cut diamond are as follows:

  1. Table Percentage: The table is the large, flat facet on the top of the diamond. The table percentage is the width of the table relative to the width of the diamond. The ideal table percentage is generally between 54% and 57%.

  2. Depth Percentage: The depth is the height of the diamond from the table to the culet (the small point at the bottom). The depth percentage is the height of the diamond divided by its width. The ideal depth percentage is typically between 59% and 62%.

  3. Crown Angle: The crown is the top portion of the diamond above the girdle (the widest part of the diamond). The crown angle is the angle between the girdle and the crown facets. The ideal crown angle is between 34.5° and 35°.

  4. Pavilion Angle: The pavilion is the bottom portion of the diamond below the girdle. The pavilion angle is the angle between the girdle and the pavilion facets. The ideal pavilion angle is between 40.6° and 41°.

  5. Girdle Thickness: The girdle is the thin band around the widest part of the diamond. The ideal girdle thickness is "thin" to "slightly thick." Girdles that are too thin can be fragile, and those that are too thick can add unnecessary weight to the diamond.

  6. Culet: The culet is the small facet at the bottom of the diamond. The ideal culet size is "none" or "very small" to ensure that it doesn't affect the diamond's appearance.

These proportions help maximize the diamond's light performance, making it appear more brilliant and sparkly. When evaluating a round brilliant cut diamond, it's also essential to consider the symmetry and polish, as well as the overall cut grade, which takes these proportions into account.

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