What’s The Ideal Cut Grade for Each Diamond Shape?

ideal cut grade
Yingjia Puk

By Yingjia Puk | Sep 30th, 2018

In our Complete Guide to Diamond Shapes, we covered the history and evolution of the ten most popular diamond shapes on the market right now. Now that we’re familiar with the shapes, which are the geometrical outlines of the stones (round, emerald, marquise etc.), we’ll explore the parameters of how each shape should be ideally cut–that is, how well an individual diamond’s facets are finished.

Depth and Table: What are they?

What does a table have to do with diamonds? The table refers to the largest facet of the diamond, found on the very top surface, which is flat like a table. Tables are measured in percentages, found by dividing the width of the table by the overall width of the diamond. These percentages are helpful when you’re looking at diamonds of different carat sizes, as you will be able to find the most ideal cut at any size.

Depth is important; for cut quality, as well as those looking to make a modest diamond appear a bit larger. Simply put, the depth is the distance from the table (the topmost surface) to the culet (the bottom point of the diamond). Depth is also described in percentages, like the table. To find the depth percentage, divide the diamond’s physical depth measurement by its overall width measurement.

Depth and Table - Diamond cut measurements

Both depths and tables are deemed acceptable within a certain range, with ideal proportions falling within each specific stone shape’s range.

For those who wish to get the largest size out of a diamond, depth matters in terms of where the weight of the stone is located. The lower the depth, the larger the diamond will appear when viewed from above, as more of the weight is in the crown (the top half) of the diamond.

What does cut grade reveal?

Cut grade is the most important factor in determining the overall appearance of a diamond. A poorly cut diamond will seem dull even with excellent clarity (VS1-VS2) and color (E-F). On the flip side, a well-cut diamond can have a slightly lower color (G-H) or clarity (SI1-SI2) and still look very beautiful, due to a diamond’s exceptional ability to reflect and refract light.

An ideal-cut diamond reflects close to 100% of the light that enters through the table and crown facets. To the observer, this reflected light is seen fire, brilliance and scintillation. GIA assigns a cut grade anywhere from Excellent (maximum light return creating exceptional sparkle and life) to Poor (light entering the diamond escape from the sides, resulting in a dull and lifeless stone).

Each shape is distinctive in its own way, so the ideal cut proportions for each shape varies from one another. For example, when looking at two one-carat diamonds in different shapes; well-cut princess diamonds are usually deeper (69% to 76%) when compared to well-cut round diamonds (58% to 64%). As a result, the round diamonds will look bigger face-up.

Round

ideal round

The ideal cut round brilliant was developed in the early 1900s by a mathematician, and is the undisputed front-runner of brilliant cuts. With 57 carefully placed facets, it can achieve the greatest amount of brilliance and light dispersion compared to any other shapes. Here are the general proportions to follow for ideal cut rounds:

Table: 54% to 57%
Depth: 60% to 63%

Princess

ideal princess

When selecting a princess cut diamond for optimum brilliance, generally avoid stones that have a table percentage greater than the depth percentage. The most ideal princess cut diamond ratio is a perfect square.

Table: 63% to 70%
Depth: 67% to 76%

Cushion

ideal cushion

Older cushion cuts have broader, larger facets, while modern cushion cuts have smaller, and more facets. This way of cutting results in a stone that resembles modern round diamonds, with added brilliance.

Table: 56% to 63%
Depth: 58% to 66%

Emerald

ideal emerald

The scintillation pattern of an emerald cut diamond is different from brilliant cut styles like rounds. Rather than little sparkles of light bouncing from the facets, the step-cut facets in emerald cuts seem to flash “on” and “off”.

Table: 61% to 68%
Depth: 60% to 65%

Oval

ideal oval

Ovals can be long and thin, or short and wide. The most pleasing length-to-width ratio is around 1.3 to 1.4. Ovals, like pear and marquise shapes, can produce a “bow-tie” effect- an undesirable dark area near the center of the diamond. This is usually more pronounced in excessively deep or shallow stones.

Table: 54% to 58%
Depth: 62% to 66%

Pear

ideal pear

For an ideal pear cut diamond, the point should line up with the apex of the rounded arc, with both sides of the arc symmetrical. It is best to choose a stone falling within 1.4 to 1.6. length-to-width ratio.

Table: 57% to 62%
Depth: 58% to 64%

Radiant

ideal radiant

A radiant cut diamond may look similar to a princess cut, but their internal facet structures are completely different. A princess cut is more linear, forming a cross pattern in the center; while a radiant cut diamond displays concentric circles radiating from the center.

Table: 60% to 69%
Depth: 59% to 68%

Marquise

ideal marquise

This is another shape where the length-to-width ratio is important, though it is always down to personal preference. The most attractive ratio is between 1.7 to 2.0.

Table: 55% to 63%
Depth: 58% to 64%

Asscher

ideal asscher

Faceted with step cuts like an emerald cut, asscher cut diamonds are an elegant and understated shape. The “X” pattern in the center is very distinctive, and the stone should ideally be cut to a 1:1 ratio.

Table: 59% to 65%
Depth: 60% to 66%

Heart

ideal heart

One of the most challenging shapes to cut, the best-cut heart shape diamonds are symmetrical with well-balanced lobes. The clef in the center should be defined, otherwise it may resemble a trilliant (triangle).

Table: 56% to 62%
Depth: 58% to 64%

Now that we’ve covered the most popular shapes’ ideal cut proportions, which diamond shape is your favorite? The most important thing to consider with fancy shape diamonds, are to see the stones in real life. A certificate–while certainly important and helpful–will not tell you exactly how the diamond looks like in person. These proportion guidelines are recommendations, as each individual’s taste will vary. Beauty ultimately lies in the eye of the beholder! It is by arming yourself with as much knowledge as possible, that’ll help you choose your most perfect diamond.

Yingjia Puk

Yingjia Puk


Yingjia is a GIA certified graduate gemologist and holds a BA from New York University She has also worked extensively with jewelry as an editor.

 
 
 
 
 
 
 
 

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