The Proportions Section of an IGI Certificate: Table, Depth, and Angles Explained

Pick up an IGI grading report for the first time and the proportions section can look like an engineering schematic. Those numbers, table percentage, depth percentage, crown angle, and pavilion angle, are the clearest window into how a diamond will actually perform in light: a table at 57% versus 65% can shift light return by a measurable margin, and the same is true for a pavilion angle sitting at 40.8 degrees versus 42.5. Each figure tells you something specific about the geometry of the cut, and together they explain why two stones with identical color and clarity grades can look completely different on a finger.

The proportions section is where a diamond’s optical story is written, going well beyond what the 4Cs alone can tell you. Once you know what each number means and what range to look for, you can use the certificate as a practical shopping filter rather than a formality.

What does the table percentage on an IGI report actually tell you?

The table is the large flat facet at the very top of a diamond. It is measured as the size of that flat top facet as a percentage of the stone’s total diameter. A round brilliant with a table of 57% means the flat top spans 57% of the stone’s width from edge to edge.

Why does that ratio matter? A smaller table allows more light to enter through the crown facets at steeper angles, which produces more fire (the colored flashes you see when a diamond moves). A larger table tends to favor brightness because more white light enters and exits straight through the top. For a round brilliant, most grading labs and experienced cutters consider 54% to 60% the sweet spot, with 56% to 58% being the range where fire and brightness are best balanced. Tables above 65% tend to look glassy and flat in person, even on a stone with an Excellent cut grade.

How does depth percentage affect the way a diamond looks?

Depth percentage is the stone’s total height (from the culet at the bottom to the table at the top) expressed as a percentage of its average diameter. A round brilliant with a 62% depth is taller relative to its width than one at 59%.

This number has two practical consequences. First, a stone with a high depth percentage carries more of its weight below the girdle, which means it will look smaller face-up than its carat weight suggests. A 1.00 ct round at 64% depth can appear noticeably smaller than a 1.00 ct round at 61% when set in a ring. Second, depth interacts directly with the angles below to determine whether light exits through the table or leaks out the sides and bottom. Depths in the 59% to 62.5% range tend to produce the most consistent light return in rounds, though the crown and pavilion angles tell the fuller story.

What do crown angle and pavilion angle control?

If table and depth are the broad strokes, crown angle and pavilion angle are the fine tuning. The crown is the upper portion of the diamond above the girdle; the pavilion is the lower cone below it.

Crown angle

The crown angle is measured between the bezel facets and the girdle plane. For round brilliants, angles between 33.7 and 35 degrees tend to produce the strongest balance of fire and scintillation. A shallower crown (below 32 degrees) can make a stone look watery. A steeper crown (above 36 degrees) can create a dark, windowed appearance in certain lighting.

Pavilion angle

The pavilion angle is where light return is most sensitive. Measured between the pavilion main facets and the girdle, this angle controls whether light that enters the stone bounces back up through the table or escapes out the bottom. The range that produces the best light return in a round brilliant is 40.6 to 41.0 degrees. At 42 degrees and above, you start to see a dark ring around the center of the stone called a fisheye. Below 40.5, light leaks out the pavilion instead of reflecting back to your eye.

These two angles also interact with each other. A slightly steeper pavilion can be offset by a shallower crown, which is why experienced buyers look at the pair together rather than either figure in isolation.

Why do these numbers matter more for lab grown diamonds?

Lab grown diamonds are cut with the same precision equipment and graded against the same optical standards as mined stones, so the proportions benchmarks are identical. But there is one practical reason proportions matter a bit more when shopping for IGI certified lab grown diamonds: because lab grown diamonds are priced lower per carat, it can be tempting to buy a larger stone and accept a weaker cut. A 2.00 ct lab grown round with a 64% depth and a 42.5-degree pavilion will look dull next to a 1.75 ct stone cut to ideal proportions, regardless of color or clarity grade.

Ouros Jewels sources IGI certified loose lab grown diamonds with cut quality built into the selection process, so the proportions data on each certificate reflects stones chosen for performance rather than just carat weight.

Proportions Tell the Story the 4Cs Cannot

Reading the proportions section of an IGI certificate gives you a level of confidence that color and clarity grades alone cannot provide. Table percentage tells you how the stone handles fire versus brightness. Depth percentage tells you how the stone will look face-up in a setting. Crown and pavilion angles tell you whether light will return to your eye or disappear out the sides. Together, those four numbers are what separate a stone that performs from one that merely passes a grading threshold. When you shop with them in mind, the carat weight on the certificate becomes a secondary detail.

Frequently Asked Questions

What is a good table percentage for a round brilliant diamond?

For a round brilliant, a table percentage between 54% and 60% is generally considered the range where fire and brightness are best balanced. Tables at 56% to 58% sit in the middle of that range. Tables above 65% tend to produce a flat, glassy appearance even when other grades are strong.

Can two diamonds with the same IGI cut grade have different proportions?

Yes. IGI’s Excellent cut grade covers a range of proportions, not a single set of measurements. Two Excellent-graded rounds can have meaningfully different table percentages or pavilion angles and still both earn the same grade. Checking the individual proportion figures lets you distinguish between stones within that grade tier.

What is a fisheye effect in a diamond and which proportion causes it?

A fisheye is a dark, circular shadow visible in the center of a diamond when viewed face-up, caused by the reflection of the girdle appearing in the table. It is most commonly produced by a pavilion angle above 42 degrees combined with a shallow overall depth. Staying within the 40.6 to 41.0 degree pavilion range avoids it.

Does depth percentage affect how big a diamond looks on the hand?

It does. A high depth percentage means more of the stone’s weight is hidden below the girdle in the setting. A 1.00 ct round at 64% depth can look noticeably smaller face-up than a 1.00 ct round cut to 61% depth, even though both weigh the same. Buyers prioritizing visual size should look for depths in the 59% to 62.5% range.

Are the ideal proportions for lab grown diamonds different from mined diamonds?

No. Lab grown diamonds share the same crystal structure and optical properties as mined diamonds, so the same proportion benchmarks apply. The ideal table, depth, crown angle, and pavilion angle ranges for a round brilliant are identical regardless of whether the stone was grown in a lab or extracted from the earth.