A diamond report draws a small map of a complex object. Table and depth describe dimensions; polish describes facet finish; symmetry describes alignment. Reading those entries together is more informative than searching for one percentage that promises beauty.
Read the diagram as a map
The table is the large facet at the top. The crown extends from the girdle to the table; the pavilion lies below the girdle. Total depth runs from the table to the bottom. The girdle is the edge where crown and pavilion meet.
On a round brilliant report, table and depth percentages relate those measurements to the diamond's diameter. Fancy-shape conventions and report layouts need their own interpretation. Always use the issuing laboratory's explanation of the diagram.
| Detail | What it describes | What it cannot establish alone |
|---|---|---|
| Table percentage | Size of the top facet relative to the reference dimension | Overall light performance |
| Depth percentage | Vertical depth relative to the reference dimension | Whether the stone looks beautiful from the top |
| Polish | Surface finish of the facets | Precise matching of their geometry |
| Symmetry | Alignment and arrangement of facets and outline features | A complete optical assessment |
Why two numbers are not enough
Crown and pavilion geometry interact. Two diamonds with similar table and depth percentages can distribute those dimensions differently, with different visual results. A total depth figure does not reveal every angle that produced it.
For example, an unusually thick girdle can retain weight around the edge. This is different from weight carried in a deeper pavilion, even if both influence overall dimensions. Read the diagram and the measurements together.
Avoid treating an online “ideal range” as a universal pass-or-fail test. A range can be a screening aid for a specified cutting style; it is not a substitute for a full assessment.
Separate polish from symmetry
Excellent polish means the facet surfaces meet that laboratory's finishing standard. Excellent symmetry concerns a different set of observations. Neither phrase means that every stone with those results looks identical.
Optical patterns seen through a specialized viewer are also not interchangeable with the conventional symmetry grade. If a seller makes a particular light-performance claim, request the evidence that supports that claim.
Turn the report into a useful viewing session
Match the report to the diamond. Check the shape, measurements and grading terminology. Then examine the clean stone while tilting it gently under more than one kind of light.
Look for an attractive distribution of brightness and contrast, rather than a permanently bright photograph. Facets naturally change as a diamond moves. Persistent dull areas deserve discussion, but one still image is not a complete diagnosis.
A worked round-diamond calculation
Consider an illustrative round measuring 6.45–6.55 × 3.96 mm, with a table width of 3.70 mm. Its average diameter is (6.45 + 6.55) ÷ 2 = 6.50 mm.
| Entry | Calculation | Result |
|---|---|---|
| Table percentage | 3.70 ÷ 6.50 × 100 | About 56.9% |
| Total depth percentage | 3.96 ÷ 6.50 × 100 | About 60.9% |
| Diameter variation | 6.55 − 6.45 | 0.10 mm |
These invented measurements explain the arithmetic; they do not define an ideal diamond or describe a Just Brilliant stone. Report rounding and the laboratory's measurement conventions can produce slightly different displayed values.
Notice what the calculation leaves out: crown and pavilion angles, girdle distribution and the interaction of individual facets. Two diamonds can share the percentages above and still distribute their geometry differently. Ask the jeweler to show where an observed feature appears on the report, rather than treating “Excellent polish” as a complete cut assessment.
Let the diagram guide your questions, then let the moving diamond answer them. Geometry provides context for what you see; it does not replace the view.
Sources: GIA diamond anatomy; GIA cut-quality research.
