Average Girth Diameter is defined as the result achieved by adding the smallest and largest diameter measurements of a round brilliant and dividing by two.

Average Girth Diameter is defined as the result achieved by adding the smallest and largest diameter measurements of a round brilliant and dividing by two.

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

Answer: (A)

When sizing a round brilliant, you measure across two perpendicular directions to capture the stone’s width in two axes because real stones aren’t perfectly circular. The smallest and largest diameters reflect this slight ovality. Taking their average gives a single, stable value that represents the stone’s overall diameter and is widely used in grading and pricing. This is exactly the definition given: (smallest diameter + largest diameter) ÷ 2. The other ideas aren’t used for size. The difference between the two diameters shows how oval the stone is, not its overall size. The sum would exaggerate the measurement, and the product isn’t a meaningful way to express a linear dimension.

When sizing a round brilliant, you measure across two perpendicular directions to capture the stone’s width in two axes because real stones aren’t perfectly circular. The smallest and largest diameters reflect this slight ovality. Taking their average gives a single, stable value that represents the stone’s overall diameter and is widely used in grading and pricing. This is exactly the definition given: (smallest diameter + largest diameter) ÷ 2.

The other ideas aren’t used for size. The difference between the two diameters shows how oval the stone is, not its overall size. The sum would exaggerate the measurement, and the product isn’t a meaningful way to express a linear dimension.