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.
In more detail
An optical device measures the stone without touching it, and the report gives the numbers in rounded steps. GIA designed its cut grade so that stones with the same rounded proportions and descriptions get the same grade. So you can estimate the cut grade of a round from this diagram.
On a grading report
On GIA's Diamond Grading Report and Dossier. IGI measures the stone with a 3D optical scan. Its report prints the key measurements and can add a graphic.
Related terms
- Table size: Table size is the width of the table as a percentage of the average diameter.
- 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.
- Girdle thickness: Girdle thickness is how thick the girdle is at its thinnest and thickest points. A report gives it as a range of words, such as "Thin to Medium".
- Culet size: Culet size is the word that a report uses for the size of the culet. The eight words are None, Very Small, Small, Medium, Slightly Large, Large, Very Large and Extremely Large.