Diamond Cut Chart: Cut Grades and Ideal Proportions
Cut decides how much a diamond sparkles, and it's the grade buyers understand least. This diamond cut chart explains GIA's five cut grades, the proportions behind a well-cut round, polish and symmetry, and how to judge fancy shapes that have no cut grade.
By Rafi Mizrahi, diamond dealer for 26 years
Cut is the only one of the 4Cs that people control. Color, clarity and carat come from nature; cut is how well the diamond was shaped and polished. It decides how the diamond handles light: brightness (white light returned to your eye), fire (flashes of color) and scintillation (the sparkle as it moves). A well-cut diamond can look bigger and whiter than a poorly cut one with better grades on paper.
GIA Cut Grades
GIA gives a cut grade only to standard round brilliants, on a five-step scale:
| Cut grade | What it means |
|---|---|
| Excellent | The best balance of brightness, fire and scintillation. Many round diamonds sold with GIA reports today are Excellent. |
| Very Good | Very close to Excellent; most people can't tell the difference face-up. Often a better price. |
| Good | Noticeably less bright. Usually a deep or shallow diamond cut to save weight. |
| Fair | Clearly dull or dark areas. Rarely a good buy. |
| Poor | Leaks light badly. Avoid for jewelry. |
Ideal Proportions for a Round Brilliant
A cut grade summarises the diamond's proportions. You'll find them on the report's proportions diagram. These are the ranges commonly cited for top-performing round brilliants:
| Measurement | Typical range | Why it matters |
|---|---|---|
| Table % | 54–58% | Too large a table trades fire for brightness; too small looks dark. |
| Depth % | 59–62.5% | Too deep looks small for its weight; too shallow leaks light. |
| Crown angle | 34–35° | Controls fire and how the crown and pavilion work together. |
| Pavilion angle | 40.6–41° | The most important angle for brightness. |
| Girdle | Thin to slightly thick | Very thin chips easily; very thick adds hidden weight. |
| Culet | None | A visible culet shows as a dot in the center. |
Polish and Symmetry
The report also grades polish (the surface finish of the facets) and symmetry (how precisely the facets are shaped and aligned), each from Excellent to Poor. For a round, the classic "triple Excellent" means Excellent cut, polish and symmetry. Very Good polish or symmetry is invisible to the eye and usually a fine way to save money; Good or below is worth a closer look.
Fancy Shapes Have No Cut Grade
Ovals, cushions, pears, emeralds and every other non-round shape get polish and symmetry grades but no overall cut grade from GIA. Judge them on proportions instead:
- •Length-to-width ratio — How elongated the shape is. Common ranges: oval 1.30–1.50, pear 1.45–1.75, marquise 1.85–2.10, emerald 1.30–1.50, cushion about 1.00–1.10 for a square look.
- •Depth and table — Very deep fancy shapes look small for their weight and can look dark in the middle.
- •Bow-tie — A dark band across the middle of ovals, pears and marquises. Some is normal; a strong one is a reason to pass.
- •Photos and video — For fancy shapes, seeing the actual diamond matters more than any number.
Our diamond shapes guide covers how each shape looks and costs.
How Cut Affects Price and Size
Cut changes price within the same color and clarity: an Excellent round costs more than a Very Good one, and a poorly proportioned diamond trades at a discount. Cut also changes how big a diamond looks. A diamond with a depth of 65% carries extra weight underneath, so it can face up like a smaller stone; see the carat size chart for typical diameters. When two diamonds have the same grades, the one with better proportions is usually the better buy, even at a slightly higher price.
Check a Diamond's Cut
Enter a GIA report number to see the diamond's cut, polish and symmetry, its proportions diagram, and quality checks that flag proportions outside the usual ranges, then unlock what they mean for its price.
Check a diamond's cut and price →