Diamond Proportions Guide: Table & Depth by Shape
Last updated 10 November 2026
Quick answer
Diamond proportions are the table, depth and angle measurements that decide how much light a diamond returns and how big it looks for its carat weight. This guide shows how to read them, with table and depth ranges for ten shapes.
How diamond proportions affect sparkle
A diamond sparkles when light enters through the top, reflects off the pavilion facets underneath and comes back out through the crown. The angle of the pavilion decides whether that happens, and when it is too shallow or too deep the light escapes through the bottom or the side before it reaches your eye.
Too shallow
Light lost through the bottom
Light meets the flat pavilion almost head-on and passes straight out through the bottom, which can leave the centre looking glassy and washed out.
Ideal
Light returned to your eye
Light reflects off one side of the pavilion, then the other, and comes back up through the crown to your eye as brightness and sparkle.
Too deep
Light lost through the side
Light reflects once, then meets the opposite side at an angle it can pass through, so it leaks out of the side and the centre can look dark.
Depth percentage alone cannot tell you which of these a diamond is. The table, crown angle and pavilion angle work together, so two diamonds with the same total depth can look different. GIA evaluates proportions in combination, along with other aspects of cut quality.
Table, depth and diameter: what the numbers mean
Table percentage
Table percentage is the width of the table, the flat facet on top, divided by the width of the diamond. On a round brilliant, the laboratory divides the average table width by the average girdle diameter.
Depth percentage
Depth percentage is the diamond’s total height, from the table down to the culet, divided by its width. Rounds use the average diameter, and most fancy shapes use the width, not the length.
Diameter and face-up size
Diameter is the width of a round across its girdle, in millimetres. Fancy shapes list a length and a width. Read those millimetres alongside carat weight, because they tell you how big the diamond looks from above.
Length-to-width ratio
Length-to-width ratio is the length divided by the width, so a 10 × 7 mm diamond has a ratio of about 1.43. It describes the outline, and the right number is whichever you prefer, longer or wider.
A worked round-diamond example
Take a round with an average diameter of 6.50 mm, a depth of 3.97 mm and a table 3.64 mm wide. Its depth percentage is 3.97 ÷ 6.50, or about 61.1%, and its table percentage is 3.64 ÷ 6.50, or 56%. Both sit inside the round ranges in the chart below, but they are measurements, not a cut grade.
Girdle thickness is worth a look too. A very thin girdle chips more easily, and a very thick one adds carat weight without adding much visible size. GIA’s round brilliant anatomy guide defines each of these measurements.
Diamond proportions chart: table and depth by shape
These are table and depth ranges for the ten most common diamond shapes. They are the ranges the retailer Brilliance publishes as “Ideal”, so use them as a first filter. They are not GIA or IGI grading thresholds, and a diamond outside them can still be a beautiful stone.
| Shape | Depth % | Table % | What to check next |
|---|---|---|---|
| Round brilliant | 59.5 to 63% | 54 to 59% | Read the cut grade and the crown and pavilion angles together. |
| Oval | 56 to 66% | 54 to 64% | Watch the centre for a persistent dark bow tie as the stone moves. |
| Pear | 56 to 66% | 54 to 64% | Compare the two shoulders, the point and brightness through the centre. |
| Princess | 66 to 75% | 66 to 75% | Some high-performing princess cuts fall outside these ranges. See the note below. |
| Radiant | 66 to 75% | 64 to 74% | Compare the facet pattern and face-up dimensions in millimetres. |
| Emerald | 60 to 72% | 60 to 72% | Look for balanced flashes across the steps as the diamond turns. |
| Cushion | 55 to 66% | 54 to 64% | Facet styles vary. Compare stones with the same cutting style. |
| Heart | 54 to 66% | 54 to 64% | Check that the lobes look balanced and the cleft is clearly defined. |
| Marquise | 56 to 66% | 54 to 64% | Check the alignment of both tips and the appearance of the centre. |
| Asscher | 60 to 72% | 60 to 72% | Compare the steps and cropped corners, including how they look in motion. |
Why there is no single “ideal proportions” chart
Retailers publish different numbers. The Diamond Pro recommends a radiant depth below 67%, while Brilliance’s range above is 66 to 75%, so the two barely overlap. Averaging them would not create a laboratory standard.
Whiteflash’s analysis of AGS Ideal princess cuts describes most of them at depths of 74 to 77%, with smaller tables favoured. A promising princess cut outside this chart is worth inspecting before you rule it out on depth alone.
Other diamond shapes and cuts
The chart covers ten shapes, and there are more. Shape is the outline of a diamond and cutting style is the arrangement of facets inside it, so an elongated cushion is still a cushion while an old mine cut is a different facet arrangement altogether. The chart above does not apply to the cuts below, which are best judged by eye and against other stones of the same style.
- Baguette and tapered baguette
- Long, narrow step cuts, sometimes tapered at one end. Compare the steps and, for a pair, how closely the two stones match in size and appearance.
- Trillion or trilliant
- Triangular outlines with straight or curved sides. Ask which cutting style the stone uses and watch it in motion, because round-diamond ranges do not apply.
- Trapezoid
- A four-sided outline, most often used as a side stone. Judge it against the setting and the stone it is paired with.
- Hexagonal and other geometric outlines
- Six-sided and other uncommon outlines need to be assessed stone by stone. The outline alone does not tell you whether the diamond has step facets, brilliant facets or a portrait-style cut.
- Old mine and old European cuts
- Antique cutting styles with different proportions from modern brilliants. Compare the facet pattern and character with other stones of the same style.
- Rose and portrait cuts
- Rose cuts have a domed, faceted top, and portrait cuts are thin and cut for transparency. Table and depth targets for modern brilliants do not describe how either is meant to look.
This is a practical selection, not a list of every proprietary cut. For more, see GIA’s antique cut guide, cutting-style definitions and Gems & Gemology’s discussion of baguette, trapezoid and trillion cuts.
How to read proportions on a grading report
Start with the cut grade, if the report has one. GIA’s overall cut grade applies only to standard round brilliants in the D-to-Z colour range. IGI introduced fancy-shape cut grading in 2022, combining proportion requirements with a visual assessment.
Read the report itself, not a retailer’s filter label. Polish and symmetry are separate grades, and Excellent in both does not make an Excellent overall cut grade.
Then watch the diamond. Compare videos shot in similar lighting, and ask for one taken away from spotlights. In elongated brilliant shapes such as ovals, pears and marquises, watch how the dark band across the centre changes as the diamond moves. In step cuts, look for facets that brighten and darken in an even pattern.
Lab-grown and natural diamonds handle light the same way, so all of this applies to both. Our diamond certification guide explains the reports, and the carat size guide shows the measurements you will see on your hand.
Frequently asked questions
- What are good table and depth percentages for a round diamond?
- A common retailer guideline for a round brilliant is a table of 54 to 59% and a depth of 59.5 to 63%. Those are published ranges, not laboratory grades, so use them as a first filter, then read the cut grade on the report and look at the stone. How the angles and facets work together matters more than passing two numbers.
- What happens if a diamond is too deep or too shallow?
- A diamond cut too shallow lets light pass out through the bottom, which can leave the centre looking glassy and washed out. A diamond cut too deep lets light leak out through the side, which can make the centre look dark, and it carries more of its weight in its depth, so it looks smaller from above than its carat weight suggests.
- Do lab-grown diamonds need different proportions?
- No. Lab-grown and natural diamonds are the same material and handle light the same way, so the same proportions apply. Judge the individual stone by its shape, cutting style, proportions and appearance, whatever its origin.
- Does a larger table make a diamond look bigger?
- Not on its own. Table percentage compares the top facet with the width of the stone, so a larger table does not mean a larger outline. To judge size, compare the face-up measurements in millimetres.
- Can an oval or emerald diamond have an Excellent cut grade?
- It depends on the laboratory. IGI introduced cut grading for fancy-shaped diamonds in 2022, using proportions and a visual assessment. GIA’s overall cut grade applies only to standard round brilliants, so check the exact report. Excellent polish and Excellent symmetry are separate grades and do not, on their own, mean an Excellent overall cut grade.
- Are these all the diamond shapes?
- No. These are ten common shapes. Baguettes, trillions, trapezoids and hexagonal outlines also exist, alongside antique cutting styles such as old mine, old European, rose and portrait cuts. A proportion chart for modern brilliant cuts cannot grade all of those designs.
Sources and further reading
- GIA: Diamond Cut, Anatomy of a Round Brilliant
- GIA: Diamond cut grading and the interaction of proportions
- IGI: Introduction of fancy-shaped diamond cut grading
- GIA: Antique diamond cuts, including old mine, old European, rose and portrait
- GIA: Gem cutting styles and outline terminology
- GIA: Summer 2009 Gems & Gemology, baguette, trapezoid and trillion cuts
