Diamond Cut and Shape Guide: How to Evaluate and Buy Cut

Diamond Cut Basics

What is diamond cut and why is it important?

Diamond cut refers to the proportions of a faceted diamond, the shape and positioning of its facets, and the general form of the stone. Cut is different from shape, which is a narrower characteristic referring only to the profile of the stone as viewed from above.

The way a diamond is cut determines how its facets will reflect light back to the eye of the observer – this is also called “light performance”. Light performance is extremely important for maximizing a diamond’s fire and brilliance.

Better-cut diamonds are more brilliant, and as a result, their inclusions are less visible. In fact, cut plays a much more important role in making a diamond look brighter than clarity.

Diamond Cut vs. Shape

People often use the words “cut” and “shape” interchangeably when talking about diamonds. However, these two terms have slightly different meanings.

Shape refers to the general outline of a stone.

On the other hand, although a specific cut implies a certain shape, the term cut technically refers to the number, arrangement, shape, and proportions of a stone’s facets.

So, a diamond’s shape tells you how a stone looks, whereas its cut gives you information as to how this shape has been achieved through cutting.

Technically, two diamonds may have the same or similar shapes, but their cuts will be considered different if their facets are arranged or shaped differently.

Although cut and shape mean different things, in most cases, a diamond’s cut tells you what its shape is, and vice versa.

Facets

When talking about diamond cuts, we should also say a word about facets. The facets of a diamond play a very important role in how it reflects light and, consequently, how much brilliance the stone gives off.

As we already saw, you can have two cuts with the same shape, but what makes them different is how they are faceted.

For example, some cuts have more facets than others; other cuts can have facets of the same shape, but they can differ in how these facets are arranged.

How are diamonds cut?

Rough diamonds are cut using special saws and laser. The goal of the cutter when shaping a rough piece of material is to create one or more faceted stones that will sell for the maximum total price. This means that some diamonds will be cut will less-than-perfect proportions if doing so will help minimize waste and maximize profits.

How does cut affect diamond size?

The way a diamond is cut can affect its dimensions and perceived size. Diamonds that are cut shallow (i.e., they are wider but their vertical distance is shorter than normal) have a greater surface and look bigger compared with stones of similar weight that are cut deeper.

This relationship between cut proportions and size is why diamonds of different cuts vary in terms of how big they look when put in a setting.

Types of Diamond Cuts

How are types of diamond cuts classified?

The round brilliant cut is considered the classic diamond cut; all other (non-round) cuts are referred to as fancy cuts.

Diamond cuts can also be divided into brilliant cuts (e.g., the round cut, the princess cut) and step cuts (e.g., the emerald cut).

Brilliant cuts have facets that are arranged in such a way as to maximize the stone’s brilliance. The classic round cut is a brilliant cut.

Step cuts, in contrast, have facets that are parallel to each other and to the stone’s edge, and they do not enhance the brilliance and sparkle of the diamond. The emerald cut is an example of a step cut.

Mixed cuts have features of both brilliant and step cuts. For example, the radiant cut is a type of mixed cut.

What is an “old European cut”?

The old European cut is a round diamond cut that used to be popular until the early 20^th century, when the modern round cut was created. Although the old European cut has the same number of facets as the contemporary round cut (58), the old European cut has different proportions – a smaller table, a higher crown, and a deeper pavilion.

Fancy Cuts

What are fancy diamond cuts?

All diamond cuts different from the classic round cut are referred to as fancy cuts. One of the most popular fancy cuts is the princess cut.

Which diamond cuts have a square shape?

The following cuts have a square or rectangular shape: princess cut, cushion cut, emerald cut, Asscher cut, radiant cut, and baguette cut.

What is an Asscher cut?

The Asscher cut is a rectangular step cut whose sides are approximately equal. It is the square variation of the emerald cut.

What is a cushion cut?

The cushion cut is a type of brilliant cut with a rectangular outline and rounded corners. There are many variations of the cushion cut, and they vary in the number, shape, and positioning of their facets. This is why it is hard to pin down many characteristics that are constant beyond the cushion cut’s general shape.

Diamond Cut Quality and Cut Grading

How is the quality of a diamond’s cut graded?

Diamond cut is graded by measuring the proportions of the stone and assigning a cut quality level to it depending on how close these proportions are to a cut standard considered ideal.

What is a fine cut and how is it different from ideal cut?

The name “fine cut” is usually used to refer to the so-called Practical Fine Cut, which is a standard that was created in Germany in 1939.

“Fine cut” is a term used mostly in Europe to denote a cut with proportions that allow a diamond to achieve maximum brilliance. In this sense, the meaning of “fine cut” is the same as “ideal cut”, and the latter term is more widely used in the U.S. There are, however, some slight differences between the perfect proportions prescribed by the fine cut standard and those of the ideal cut.

What Is the Difference Between Ideal Cut and Fine Cut?

Although the American ideal cut and the European fine cut both refer to diamond proportions that maximize brilliance, these two standards differ slightly in the ideal measurements they recommend.

Here are the biggest differences:

Crown Height

A diamond shaped according to the American ideal standard should have a taller crown than that of a fine-cut diamond. (The crown is the top part of a round diamond and is separated from the bottom part by the stone’s edge, or the girdle.)

The American Standard recommends that diamond crown height be 16.2% of the diameter of the girdle, while the fine cut standard stipulates 14.4%.

Table Diameter

The table is the flat top of a round diamond, and its diameter is also measured as a percentage of the girdle’s diameter.

The American Standard says that the table should have a diameter that is 53% of that of the girdle.

The proportion recommended for this measure by the fine cut standard is 56%.

There are other differences between the ideal cut and the fine cut, but they are insignificant.

As you can see, these two cuts are pretty similar, and it is unlikely that you would be able to spot a difference between an ideal- and a fine-cut diamond in terms of brilliance.

Can a diamond cut be too deep or too shallow?

The depth of a diamond is measured as the vertical distance from its top facet to its bottom (total depth) or as the distance from the girdle to the bottom (pavilion depth). It is accepted that a pavilion depth of around 43% is ideal and that a total depth of 57.5% to 59.45% is the most desirable for round diamonds.

Stones that are too shallow or too deep relative to these standards will lack the brilliance diamonds with closer-to-perfect proportions have. In addition, when in a setting, deep-cut diamonds look smaller for their carat weight compared with shallower-cut stones, which have more visible surface area.

What Does “Deep Cut” Mean?

The so-called ideal diamond cut dictates what the optimal depth of a round shaped stone should be. This optimal depth is one of the prerequisites for maximum brilliance.

When a diamond’s depth is too high relative to the stone’s width, it is said that this diamond is cut too deep, and its cut is often referred to as “deep cut.”

Why Is a Deep Cut Problematic?

A deep cut detracts from the brilliance and sparkle of a diamond.

Stones that are cut this way look less lively and have lower brightness compared with more proportional diamonds. The deeper the cut of the stone, the duller it looks.

Another problem with deep cuts is that when such diamonds are set in a mounting, they look smaller than ideal-cut diamonds of the same carat weight.

This is so because in order to achieve a greater depth, the cutter has sacrificed some of the stone’s width.

When the diamond is put in the setting, the additional depth is hidden in it, and the only part visible is the diamond’s top, which is smaller than normal.

What is a “spread diamond”? Should I buy spread diamonds?

Spread diamonds are stones that have been cut much shallower than diamonds whose depth is close to ideal. As a result, spread diamonds are wider than better-cut stones of similar carat weight. This is what makes spread diamonds look bigger when put in a setting.

If you care about how big your diamond looks but your budget is limited, a spread diamond may be a viable choice. However, keep in mind that spread diamonds have reduced brilliance, as their sub-optimal depth causes most of the light entering them to leak out through the bottom instead of being reflected back to the eye of the observer.

How is the quality of princess cuts graded? What are the most important quality factors I should be evaluating?

Although there is not such a robust grading system for princess cuts as there is for round cuts, the way the quality of the princess cut is judged is essentially the same – by looking at its key elements (such as the girdle, the table, the crown, and the pavilion) and measuring them to calculate their proportions.

The most important quality factors for a princess cut are its total depth relative to the stone’s width, the width of the table relative to the width of the girdle, the stone’s length-to-width ratio, and the thickness of the diamond’s girdle.

How is the quality of radiant cuts evaluated?

The quality of radiant cuts is assessed by measuring their total depth, table width, girdle width, and girdle thickness. The most important quality factors derived from these measurements are the cut’s table ratio (table width to girdle width) and total depth ratio (total depth to girdle width).

What Is an Ideal Cut?

When referring to round-cut diamonds, a cut is considered ideal if its proportions allow the stone to retain and reflect as much light as possible back to the eye of the observer, maximizing the brilliance and sparkle of the diamond.

On the other hand, the further a diamond’s proportions are from the measurements that are considered ideal, the more of the light that enters the stone leaks out of it.

Since the facets of poorly cut diamonds are not well aligned to retain maximum light, such stones appear dull and lifeless.

Different Ideal Cut Standards

Although it may seem that the definition of ideal cut is uniform, there is actually no universal agreement as to what the exact ideal proportions should be.

In reality, there are at least half a dozen standards for the measurements of the ideal cut.

The most widely used benchmarks today are the American Ideal Cut, the Practical Fine Cut, and the Scandinavian Standard.

The first one is used in North America, and the other two are mainly used in Europe.

Key Diamond Cut Dimensions and Proportions

One of the most accurate ways to determine the quality of a diamond’s cut is to examine some of its key measurements and calculate proportions.

But before you start checking diamond dimensions, you should be familiar with several terms regularly mentioned when measuring and evaluating diamond cut:

Girdle: This is the outer edge of the stone, and most diamond proportions are expressed as percentages of the girdle’s diameter (for round stones) or width (for non-round shapes).

The girdle itself can be graded on its thickness, and cuts with extremely thin or extremely thick girdles are undesirable; anything between these two extremes is acceptable, with the ideal girdle being thin to slightly thick.

Culet: This is the facet at the very bottom of the diamond. A stone can have no culet at all, and this is also acceptable.

The ideal culet is very small to small, with medium and big culets being less desirable.

Table percentage: The table is the topmost facet of the stone, and table percentage is calculated by dividing the table diameter or width by the diameter or width of the girdle.

Depth percentage: This is the distance from the table to the bottom of the stone divided by the girdle diameter or width.

Round Cut Ideal Proportions

Although there are different standards for ideal round cut, the proportions they use as guidelines are more or less similar.

The first thing you should know about the ideal measurements is that they are expressed as a percentage of the diameter of the diamond’s girdle, which is simply the stone’s edge and is also its widest part.

Let’s look at the most important measurements for an ideal-cut diamond. The numbers are given as ranges that include the standards of the most widely used benchmarks:

Table diameter: 53%-57.5% (This is the diameter of the diamond’s flat top, i.e. the table.)

Crown height: 14.4%-16.2% (This is the vertical distance from the girdle to the top of the stone; the crown is the upper part of the diamond, from the girdle to the table.)

Pavilion depth: 43.1%-43.2% (This is the vertical distance from the girdle to the bottom of the diamond; the pavilion is the lower part of the diamond, from the girdle to the lowest point.)

So, using the above numbers to derive a rule-of-thumb benchmark, we can conclude that an ideal-cut diamond should have a top that has a width of 53% to 57.5% of the girdle, a pavilion that is around 43.1%-43.2%, and a crown that is around 14.4%-16.2% of the girdle diameter.

The total height of an ideal diamond, measured from its flat top to the stone’s pointed bottom, will be around 57.5%-59.4%.

If you are shopping for a diamond, you most likely won’t need to measure all these values yourself: They will be included in the diamond’s grading report, and you should look them up. It is not recommended to buy diamonds that do not come with such a certificate that verifies their quality.

What about other diamond cuts?

Unlike the classic round cut, most other cuts do not have as detailed, precise, and widely accepted benchmarks against which to measure cut quality. There are guidelines, but they are much looser, and they vary from cut to cut.

What’s more, many grading labs do not grade the cut of non-round diamonds. The best way to evaluate the cut of such stones is to compare them and see which one has more brilliance as well as which diamond looks better (or even bigger) when worn.

Below you can see the ideal proportions suggested for the most popular non-round diamond cuts.

Oval Cut, Marquise Cut, Pear Cut, and Heart Cut Ideal Proportions

The recommended dimensions for the oval cut also largely apply to the cuts that are derived from it: the marquise cut, the pear cut, and the heart cut.

For all these cuts, the ideal table percentage is in the 52%-64% range. A value as low as 51% or as high as 68% is also acceptable and is a sign of a good cut. Cuts with a table percentage of 50% and lower or 69% and higher are not considered top quality.

The recommended depth percentage for the oval cut and its derivatives is between 58% and 62%, with values as low as 53% and up to 70% also considered acceptable. Depth percentages lower than 53% and higher than 70% are not recommended.

The length-to-width ratios recommended for these cuts are the following:

• Oval: Between 1.25 and 1.60; ideally in the 1.30-1.50 range.
• Marquise: Between 1.65 and 2.30; ideally in the 1.85-2.00 range.
• Pear shaped: Between 1.35 and 1.80; ideally between 1.40 and 1.55.
• Heart shaped: Between 0.80-1.10; ideally between 0.90 and 1.05.

Princess Cut Ideal Proportions

Ideally, the table percentage of a princess cut should be in the 60%-75% range. It is not recommended to buy a princess cut whose table percentage is higher than 80% or lower than 56%.

The ideal depth percentage for this cut is between 65% and 75%. Values outside of the 60%-80% range are not considered desirable.

Princess cuts with a length-to-width ratio in the 1.00-1.05 range are the most desirable – i.e., such stones look square, whereas higher ratios result in a more oblong look.

Cushion Cut Ideal Proportions

The ideal table percentage for cushion cuts falls anywhere between 58% and 70%. Values higher than 71% and lower than 56% are not desirable.

The recommended values for the depth percentage of cushion cuts are similar: ideally, in the 58%-70% range; lower than 56% and higher than 71% – not recommended.

The optimal length-to-width ratio for non-square cushion-cut diamonds is between 1.10 and 1.30.

Radiant Cut Ideal Proportions

The table percentage of an excellent or very good radiant cut should be in the 60%-70% range. Values that fall between 54% and 74% are also acceptable, while table percentages beyond this range are not recommended.

The ideal depth percentage for a radiant cut is also in the 60%-70% range. Values below 57% and above 74% are not desirable.

The most sought-after length-to-width ratio for non-square radiants is in the 1.10-1.40 range.

Emerald Cut and Asscher Cut Ideal Proportions

The emerald cut and the Asscher cut are basically the same – the latter is just the square version of the former.

A table percentage in the range of 60%-70% is considered best for these cuts, and values as low as 55% and as high as 73% are still considered good. Avoid Asscher and emerald cuts whose table percentage is lower than 54% and higher than 74%.

Depth percentage in these cuts should ideally be between 60% and 70%. Values lower than 57% and above 74% are not recommended.

For emerald cuts, the most preferred length-to-width ratios fall in the 1.20-1.80 range.

The ideal length-to-width ratio for Asscher cuts is between 1.00 and 1.05.

How Diamond Cut Works

Cut affects three major characteristics of a diamond that define how light interacts with the stone: brilliance, dispersion and scintillation.

Brilliance is seen when light entering the stone is reflected back to the eye of the observer. If a diamond’s depth (or height) is too high or too low, the light going into the diamond will not be reflected back to create brilliance but will instead leak out of the stone, remaining unseen.

As a result, the brilliance of too deep or too shallow diamonds is poor.

Dispersion is when the structure of the diamond breaks down the entering light into a spectrum of colors. The result is visible as play of colors when looking at the diamond and is also called “fire”.

Scintillation is the ability of a diamond to sparkle in intermittent flashes as you move it before your eyes. A well-cut stone exhibits a lot of sparkle, whereas a poorly cut one looks much less lively.

How Important Is It to Buy an Ideal Cut?

The closer the cut of a round diamond is to the ideal cut, the higher the stone’s brilliance will be.

Diamonds with poor cuts look less bright and appear lifeless, not to mention that because of the diminished brightness, their flaws and color tints become more visible.

So, it is usually a good idea to pay more money for an Ideal/Excellent cut if you can afford it. In any case, don’t go lower than one grade down from Excellent/Ideal – i.e. don’t buy a cut that’s rated lower than Very Good unless you are fine with the diminished brilliance that comes with the price savings.