How is a diamond's depth percentage defined?

• A. Girdle diameter divided by total depth × 100
• B. Table width divided by depth
• C. Crown height divided by pavilion depth
• D. Total depth divided by girdle diameter × 100

Answer: (D)

Depth percent measures how tall a diamond is relative to its width, expressed as a percentage. It’s defined as the total depth (the distance from the table down to the culet along the center line) divided by the girdle diameter (the width across the girdle, averaged around the stone), multiplied by 100. This proportion matters because it affects how light is returned to the eye; a stone that is too deep can look dark from top, while one that is too shallow can leak light from the sides. The standard definition uses total depth in relation to the girdle width, which is why dividing total depth by girdle diameter and multiplying by 100 is the correct formulation.