A diamond's proportions are the angles and percentages that describe its shape in profile. They cover the table, crown, pavilion, star and lower half lengths, girdle, culet and total depth.
In more detail
Each proportion is an angle or a percentage of the average diameter. So you can compare stones of any size directly. The proportions set how a stone handles light and most of its cut grade. Two values that are each in range can still lower the grade as a pair.
On a grading report
On the proportion diagram of GIA and IGI reports.
Related terms
- Proportion diagram: The proportion diagram is a side-view profile of the stone, drawn to its measured proportions. It shows the table, depth, crown, pavilion, star and lower half lengths, girdle and culet.
- Average diameter: The average diameter of a round is the mean of its minimum and maximum diameters, measured across the girdle.
- Total depth: Total depth is the height of a stone from table to culet as a percentage of its average diameter. It equals crown height + girdle thickness + pavilion depth.
- Crown angle: The crown angle is the slope of the bezel facets, measured against the plane of the girdle.
- Pavilion angle: The pavilion angle is the slope of the pavilion mains, measured against the plane of the girdle.
- Cut grade: The cut grade rates how well a diamond's proportions and finish work, from Excellent to Poor. GIA gives it only to standard round brilliants in the D-to-Z color range.