Average Girth Diameter is defined as the mean of the smallest and largest diameter measurements of a round brilliant.

• A. The result achieved by adding the smallest and largest diameter measurements of a round brilliant and dividing by two.
• B. The sum of the smallest and largest diameter measurements.
• C. The maximum diameter of the girdle.
• D. The difference between the smallest and largest diameter.

Answer: (A)

Average girth diameter is the arithmetic mean of the smallest and largest diameter measurements of a round brilliant. To obtain it, add the two measurements and divide by two. This provides a single representative width that accounts for slight variations around the girdle, rather than relying on a single edge-to-edge value. It’s not the sum of the measurements (which would overstate size), not the maximum diameter (which uses only one extreme), and not the difference (which shows how far apart the measurements are).