The proportion diagram on a GIA report is a small side view of the diamond, drawn to the stone's measured proportions. It shows how the table, the crown, the girdle, the pavilion and the culet sit together, and it puts those measurements in one place rather than leaving you to imagine the profile from a list of figures. The Gemological Institute of America includes this graphic on a diamond grading report, and it is one of the most useful parts of the paperwork once you are comparing stones.
What the diagram shows
GIA describes it as a diagram of the diamond's proportions, and also uses it to record the girdle thickness, which can affect durability. In GIA's published cut material, the graphic is scaled to depict the actual parameters of the stone: table size, total depth, crown angle, crown height, pavilion angle, pavilion depth, star length, lower half length, girdle thickness and culet size. The crown is the upper part of the diamond, from the table down to the girdle. The pavilion is the lower part, from the girdle down to the culet. Seeing those two parts drawn in profile makes it easier to understand the percentages explained in our guides to table and depth and to girdle and culet.
How it relates to the cut grade
For a standard round brilliant, GIA considers these proportions together, along with polish and symmetry, when it assigns a cut grade. No single figure on the diagram tells the whole story, which is why GIA is clear that proportions are not judged in isolation. Most fancy shapes do not receive that same cut grade, but the report still usually includes the measurements, and often a diagram, which we still read carefully with you. Our guide to why cut matters explains the grade itself.
How we use it with you
When we shortlist stones, we set the diagrams side by side as well as the grades. A deeper pavilion or a thicker girdle can be easier to see on the graphic than in a table of numbers. We still look at the diamond on a video consultation, because two stones with similar proportions can return light a little differently. Our guide to how to read a GIA certificate sets the diagram in the context of the rest of the report, including the clarity plot.
Nothing is made until you approve the design and the stone in writing. A 70 percent deposit is paid then, making time is 5 to 6 weeks, and the ring is UK hallmarked before insured, tracked FedEx delivery. If you would like to go through a report with us, get in touch or browse the diamonds we can source.
Frequently asked questions
What is the proportion diagram on a GIA report?
It is a small side view of the diamond, drawn to the stone's measured proportions. GIA uses it to show the table, the depth, the crown and pavilion, the girdle and the culet together on one graphic, rather than as a list of numbers alone.
What measurements appear on the diagram?
On a GIA Diamond Grading Report the graphic is scaled to show table size, total depth, crown angle and crown height, pavilion angle and pavilion depth, star length and lower half length, girdle thickness and culet size. Each figure describes a part of the profile.
Does the diagram replace the cut grade?
No. For a standard round brilliant, GIA uses these proportions, together with finish, when it assigns a cut grade. Most fancy shapes do not receive that same cut grade, but the measurements and the diagram are still useful to read.
Should you choose a diamond from the diagram alone?
No. The diagram is a clear picture of how the stone is built, but two diamonds with similar figures can still look different in the hand. We look at the report and at the diamond on a video consultation before you approve the stone in writing.