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Diamond Proportion: Everything You Need to Know

Diamond Proportion: Everything You Need to Know

As you know, a diamond’s cut is an essential aspect in deciding its price. Of course, experts will take the stone’s proportions into account when estimating the cut’s excellence, too.

While diamond proportion may appear to be a jumble of numerals and percentages, ignoring it may result in a diamond with no brilliance at all.

So, what is the significance of diamond proportion in all that?

Knowing how to read those numbers grants you a superpower of sorts – the ability to detect the existence and degree of brilliance in diamonds. In simpler words, the diamond proportion factors assist you in determining whether or not your stone has an excellent cut.

You’ll also be able to form your own opinion regarding the diamond’s value. So, let’s figure out how to read diamond proportion percentages and put that knowledge to good use!

What Exactly Is Diamond Proportion?

Diamond proportions are just different samples of angles and lengths in diamonds. These measurements, however, are not random. They specify the diameter of a gem, as well as the depth and width of its sections – such as a crown, table size, and pavilion angle – and height.

These dimensions are commonly defined in millimeters or percentages.

The anatomy and geometry of diamonds are determined by various sets of ratios. So, the stone has a superb cut and excellent attractiveness if it has an ideal set of length, breadth, and depth ratios for its form and carat weight.

Furthermore, diamond proportions affect a jewel’s capacity to reflect light effectively. That is due to the mesmerizing movement of light in the gem – whether colored and white light or alternating flashes – caused by precisely cut angles and lengths.

That is how stone proportions affect fire, brightness, and scintillation and how they become the primary characteristics that define cut excellence and diamond pricing.

Calculating Diamond Proportion

You must do some math to obtain the specific diamond percentage values. More precisely, the proportion of pavilion depth, table size, and crown height in relation to the diameter of the stone should be obtained.

The stone’s diameter appears in every diamond proportion ratio. It’s critical since the gems vary in shape and carat size – and that means that including size in these calculations improves the accuracy of the derived values.

Even the smallest modification in any of the diamond proportions damages the precious stone’s delicate brilliance. That’s because cut quality relates to the capability of light to flow through the stone surface and back into the spectator’s eye. 

As a result, any change in their interaction halts the process of light reflection and “turns off” the diamond, causing it to become dull and discolored.

Diamond Width

Diamond width is the distance between the girdles of a gem. The breadth of a round diamond equals its diameter. This diamond parameter, as you may know, is utilized to compute all of the cut-related proportions in a diamond. 

The width of different gem shapes is utilized as a part of the length to width (L/W) ratio. It mostly reveals how well-proportioned a diamond shape is. To understand what it means, divide the entire length of a stone by its width. For example, if a diamond is 5 mm long and 3 mm wide, the length to width ratio is 1.67.

Below are the suggested length-to-width ratios for every diamond form:

Diamond ShapeSuggested L/W ratio

Diamond Table

For those unfamiliar with the term “diamond table width,” it refers to a jewel’s top (“face-up”) surface – or the greatest facet visible when viewing the stone from above. When you compare multiple diamonds, you’ll discover that they all have one thing in common: A plain, table-like surface.

To calculate the table dimensions, divide the table breadth by the total stone diameter, which is the broadest width of a fancy-shaped diamond.

For illustration, lengths of 3 mm and 4 mm indicate that the table size is 75%. This interpretation is overly simplistic, but: Light is lost within a diamond and bounces back unpredictably through the sides, never reaching the table. As a result, even if the width and depth requirements are correct, the cut is poor.

If the table width is 2 mm and the gem diameter is 3 mm, the table value is 66%. That is already excessive. No matter how perfect the breadth and depth are, that stone doesn’t reflect light and has poor cut excellence, leaving the diamond looking lifeless.

So, those are the reasons why a diamond table size is one of the essential aspects of the look of any diamond. You’ll find the appropriate table percentage ratio for some of the most popular diamond shapes below. Since diamonds are more intricate than a few digits, these ranges should merely be used as suggestions, though.

Diamond ShapeIdeal Table Range (%)
Round 54-57
Marquise 53-63

Note that, outside of these parameters, the diamond table can have a detrimental impact on the appearance of the gemstone.

Diamond Depth

Diamond depth proportion is computed by dividing the stone’s height by its width. The height, in this case, refers to the length of the gem from top to bottom, at its base. For instance, if a diamond has a depth of 4 mm and a width of 5 mm, the depth percentage will be 80%.

A diamond with a reduced depth percentage seems more prominent owing to its greater width – but it frequently has a gloomy appearance since it does not reflect light as effectively. 

Regarding the sparkle, the light will travel through the stone without leaving a mark. And a lack of sparkle and brightness indicates a lack of cut quality. A diamond with a significant depth percentage leaks light off the bottom, making it seem lifeless. 

But, all these aspects together – the depth, table, and breadth of a diamond – contribute to how effectively it refracts and reflects light. So, yes, it is critical to locate a diamond with optimal cut ratios in each section.

Aspects Affecting Diamond Proportion

The diamond width, total depth, and table width are parameters that influence the gemstone’s proportions. But other aspects like the shape, size, cut, and angle of each facet determines how effectively a diamond interacts with light.

Here are some important factors that affect diamond proportion: 

  • Table width refers to the length and breadth of a diamond’s table or top surface area.
  • Total depth is the length of a diamond from the culet to the table.
  • Crown angle is the inclination of a gem crown from the top of the girdle to the border.
  • Crown height is the distance between the top of the girdle and the table.
  • Pavilion angle specifies the angle between the bottom of the girdle and the border of a stone pavilion.
  • Girdle thickness represents the height of the girdle, the belt that divides the crown from the pavilion.

Ideal Diamond Proportions

Evaluating the aforementioned characteristics might help you determine whether or not the gem you’ve chosen has an appropriate cut. We’ve provided the precise diamond proportions for round-cut diamonds below:

Table Percentage54 – 57 %
Depth Percentage59 – 62.6 %
Length to Width Ratio1.0 – 1.03
Girdle ThicknessThin to Slightly Thin

All of these aspects contribute to the diamond’s charm and brightness. And by adhering to these perfect diamond dimensions, you’ll end up with a magnificent gemstone that both absorbs and reflects light.

Begin your search for the ideal proportions among GIA and AGS Excellent and Ideal cut gems. Narrow down your choices based on the suggestions above since some “Excellent” and “Ideal” cut diamonds might still fall outside of these parameters.

The Origin Of The Ideal Cut

In 1919, Marcel Tolkowsky first proposed the concept of desirable diamond proportions. He was a Belgian engineering graduate from a diamond-cutting family. Tolkowsky published a dissertation on the dimensions of round brilliant cut diamonds in his book “Diamond Design.” 

Relying on the physics of light, his equation concentrated on the proportions that would release the greatest fire and brightness, yet the idea of scintillation received little emphasis in his thesis. It is worth noting that numerous American cutters, notably Henry Morse, had been cutting to the same standards that Tolkowsky had found for many years – before his renowned research was even published.

But when the American Gem Society’s lab (AGSL) specialized in cut excellence debuted back in 1996, they used Tolkowsky dimensions as the foundation for their Ideal Cut classification.

Specifications For The Tolkowsky Cut

After Tolkowsky’s cut criteria went public, the phrase “round brilliant” became popular, as well. Tolkowsky noted that to get the finest light reflection in a round-cut gemstone, 25 pavilion facets and 33 crown facets should be ideally balanced. 

He additionally specified the angles and depths shown below:

Total Depth59.3 %
Diameter53 %
Crown Angle34.5 %
Pavilion Angle40.75 %
Pavilion Depth43.1 %

Grading laboratories are no longer as rigorous with diamond percentage values, resulting in a somewhat broad range of numbers for the perfect cut. 

For instance, as previously indicated, the optimal diamond depth for the round brilliant cut spans from 59.3% to 62.6%, giving a diamond cutter more leeway than an overly precise 59.3% depth requirement.

Nonetheless, this depth is not simple to accomplish – and the stone still looks exceptional.

Related Read: Who Is The Best Diamond Cutter In The World?

Crown Angle

The crown represents the top section of the diamond, located beneath the plain top table and “crowning” the pavilion cone. However, the true crown angle of the gem relates to the level of separation between the table and the girdle of the diamond.

How significant is the crown angle?

The crown angle has a considerable impact on a diamond’s frontal look. An optimal crown angle redistributes light – often known as diamond fire – when paired with perfect overall proportions. 

So, in that sense, the crown angle is a vital factor in determining the proportions of a diamond.

Wondering how to calculate the crown angle? Here’s a quick explanation:

  1. Divide the stone’s table by 100.
  2. Take your answer and subtract it from 1.
  3. Multiply the result by 50.
  4. Divide the crown depth by the above-mentioned answer.
  5. Press the Tan – 1 key on a scientific calculator. The exact crown angle stated in degrees will be provided as the solution.

Pavilion Angle

When examining a diamond’s proportions, some individuals prefer to utilize the pavilion angle rather than the pavilion depth percentage. In reality, they are only two perspectives on the same issue. The larger the depth percent, the sharper the angle.

The pavilion angle is responsible for the diamond’s sparkling, astonishing look. You see, the angle reflects light from one end of the stone to the other before reflecting it forth, resulting in stunning prismatic light. 

Diamonds that do not have the appropriate pavilion angles – or that are either too deep or too flat – will be unappealing. To get the pavilion angle, do the following:

  1. Measure the diamond’s pavilion depth and input the result into a calculator.
  2. Then divide the result by 50.
  3. Then, on your calculator, hit the Tan – 1 key, and you’ll get the real pavilion angle in degrees.

The Perfect Ratio Between Crown And Pavilion Angles

An excellent-cut gemstone is proportioned so that virtually all of the light entering the diamond is reflected back to the spectator’s eye. A seemingly minor alteration in the pavilion or crown angle may create a significant change in a diamond’s brilliance, fire, and sparkle.

Diving even further, there is an ideal equilibrium that can be struck among crown and pavilion angles to produce a diamond with excellent light performance.

As previously stated, the pavilion angles, in particular, have a critical influence in defining how much light is reflected in the spectator’s eye. A shallow pavilion angle, for example, will lead to a shallow stone. And an overly steep pavilion angle, on the other hand, will produce a deep diamond.

Nevertheless, to a certain extent, a somewhat too shallow or too steep pavilion inclination can be compensated for by an “acceptable” crown angle. Scientists have discovered that a pavilion angle of 40.6° to 41.0° generally delivers the highest brightness to a diamond.

As a result, a somewhat too shallow pavilion angle of 40.5° should preferably be compensated for by a higher crown angle of, let’s say, 35°. The same would be for a diamond with a relatively steep pavilion angle of 41°, which should be adjusted by a crown angle of 34°.

If you don’t overlook these factors, you can be confident that you will get a gem with remarkable light performance!


So, let’s summarize this highly important gemstone aspect – diamond proportion

Keep in mind that diamond proportion is more than a hodgepodge of numbers and percentages. It is an extremely important element – and if you overlook it, you could wind up with a stone that has no shine at all. 

The color and clarity scores are generally deemed essential, and you may easily disregard the proportions – but do so at your own risk. Therefore, while selecting a diamond, try to ensure that it is within the proportions indicated in this article.

Of course, it won’t be a problem if the gemstone is slightly outside the perfect dimensions range. However, the more a diamond is within these proportions, the greater its light performance.