A graded cut is a diamond whose overall cut quality has been independently assessed and assigned a grade by a recognized gemological laboratory. The grading standards are rigorous, methodology-based, and consistent across stones submitted to the same lab. A graded cut is the gold standard because it removes subjectivity and salesmanship from the quality assessment — the grade is what it is, regardless of what a retailer claims about the stone.
The uncomfortable reality for most diamond buyers is that the majority of diamonds sold — every oval, every cushion, every emerald, every pear, marquise, princess, Asscher, radiant, and heart cut — are not graded for cut quality. GIA, the most widely used and trusted grading lab, assigns an overall cut grade exclusively to the standard round brilliant. For every other shape, the GIA grading report contains polish and symmetry grades, but no assessment of whether the stone's proportions produce good light return.
| Shape | GIA cut grade | AGS cut grade | Buyer alternative |
|---|---|---|---|
| Round Brilliant (standard 58-facet) | ✓ Excellent–Poor | ✓ Ideal–Poor | Best-graded shape; use GIA or AGS report |
| Princess | — | ✓ AGS grades some | Evaluate depth, table, symmetry; use AGS when available |
| Oval | — | — | Proportion evaluation + ASET/IdealScope imaging |
| Cushion | — | — | Proportion evaluation; request light performance tools |
| Emerald | — | — | Depth %, table %; in-person evaluation essential |
| Asscher | — | — | Depth %, table %; clarity evaluation crucial |
| Pear | — | — | Proportion evaluation; ratio, depth, bow-tie assessment |
| Marquise | — | — | Proportion evaluation; ratio, depth, bow-tie assessment |
| Radiant | — | — | Proportion evaluation; similar to cushion methodology |
| Heart | — | — | In-person evaluation; symmetry critical for shape integrity |
| Old European | — | — | GIA grades as modified round; no cut grade issued |
| Old Mine | — | — | GIA grades as antique; no cut grade issued |
| Rose Cut | — | — | No current grading standard; rely on craftsmanship assessment |
| Baguette | — | — | Step cut; clarity evaluation more important than cut grade |
When a cut grade is not available — which is the case for virtually every fancy shape — buyers have three practical substitutes. First, proportion evaluation: checking that depth percentage, table percentage, and length-to-width ratio fall within accepted ranges for that shape. These specifications are listed on every cut page on this site. Second, light performance imaging: tools like ASET (Angular Spectrum Evaluation Tool), IdealScope, and proprietary platforms from dealers such as Whiteflash, Brian Gavin, or James Allen provide photographs or computer models showing actual light return. Third, in-person observation: evaluating the stone under various lighting conditions — diffuse overhead light, directional light, candlelight — is the ultimate arbiter of whether a stone performs the way you need it to.
Some online retailers have begun using their own proprietary cut quality assessments for fancy shapes. These can be useful but should be approached with appropriate skepticism — they are developed by the same parties who benefit from the sale. Third-party tools (ASET imaging, Sarine Light) are preferable because they are produced by independent instruments rather than by the seller's own evaluation team.
If you are buying a round brilliant, a cut grade from GIA or AGS is available and should be your first checkpoint. If you are buying any other shape, there is no equivalent third-party cut grade — and you should treat every retailer's claim about cut quality with appropriate scrutiny. Proportion ranges, ASET imaging, and in-person evaluation are your best tools. The absence of a cut grade is not a flaw of the stone; it is a gap in the grading infrastructure that buyers need to understand and work around.