Ideal Diamond Proportions

super ideal cut diamond proportions

Bottom Line Recommendations

  • Up to 20 percent of the light that enters a diamond will be reflected and will not enter the diamond. Of the remaining 80 percent, some will be lost through the pavilion. This is why you should aim for a stone with the most ideal proportions in order to maximize the light reflection. Take a look at a good example of a cushion cut here.
  • If you want to strike a good deal, go for a stone with a shallow depth. Most of the weight will be distributed towards the edges making it appear larger than it is.
  • Choose a diamond with an ideal size table as you can see here. It should not be too large and neither should it be too small. Any of these can interfere with the light reflection causing the diamond to be less brilliant.
  • When evaluating the stone, you can find all the information you need about the cut quality of the stone from the diamond report. Note, however, that there are other factors affecting the performance and appearance of a diamond. Because of this, it is always a good idea to view 360-degree videos of the diamond.
  • We recommend buying your diamonds from James Allen or the Blue Nile. They offer the best quality videos and images and also some of the best services.

James Allen Diamonds
When buying a diamond, you will focus mainly on the 4Cs. These are the color, carat weight, clarity and cut of the stone. Of these, it is the cut that is the most important.

It is the cut of the diamond that contributes most to its fire and brilliance and gives it its scintillation. When judging the cut of your chosen stone, several factors need to be considered.

You will need to evaluate the cut by checking its proportions, craftsmanship, and symmetry of the stone. To some, it might seem complicated.

When cutting the diamond from the rough stone, it is the skill of the cutter that will determine the right balance between the maximum yield and the optimal cut. The idea is to maintain as much of the stone as possible and to get the largest diamond from the rough stone.

After all, most buyers will be willing to spend more money on a larger stone than a smaller stone. The challenge is on the cutter as it is easy to get tempted to sacrifice the quality of the cut for the weight and size of the stone.

When evaluating the cut of the diamond, you can tell which stone was cut with priority given to size instead of the quality of the cut itself.

To better explain the situation, consider two diamonds cut from the same rough. A diamond cut that is too deep will be larger as less of the rough will be wasted. The cutter is therefore likely to get a larger profit from the stone. The downside is that the cut quality might below.

On the other hand, paying more attention to the quality of the cut may result in a smaller diamond and while it may ask for a lesser price than a larger diamond, it’s per carat premium will be higher. However, it may end up being costlier as more of the rough is lost.

The Diamond Proportions

Diamond proportion refers to the geometry of the stone. In other words, it is the ratio and the angles of the facets and the measurements of the diamond. Diamond graders will compare a stone with the table size, crown height, and pavilion depth and compare this with the diameter of the stone through the girdle.

Ultimately, you can think of the diamond proportion as to how the angle of the facets, the size of the diamond and the shape of the diamond relate. It is possible to play around with different factors. Different combinations will result in differences in light action.

Something to keep in mind at all times when evaluating the diamond is that whenever it is exposed to light, up to 20% of it will be reflected and will not enter the stone. The remaining 80% will go through the diamond but some of it will also come out through the bottom.

The best-cut diamond will have the facets placed at the most optimum angle to maximize the amount of light that will be reflected through the crown and to the observer. This ultimately means minimizing as much as possible the amount of light that escapes through the bottom of the stone.

Three things happen to light whenever it hits a diamond. The first is that it could reflect. This is the bouncing back of the light. It can also refract which is the bending of light. The angle of the facet determines whether most of the light reflects or refracts.

The Diamond Depth %

The distance between the table of the stone and its culet is referred to as the depth. This is when viewing the diamond from its side. The depth of a diamond is expressed in millimeters.

To get the depth percentage, you will take the depth of the stone and divide it by the width. A low depth causes a diamond of the same carat weight to appear larger than it is. This is because most of the stone will be concentrated in its width than at its depth.

The diamond depth percentage will determine the overall proportions of the stone and will affect how light bounces off the facets of the diamond.

The diamond depth has a big impact on how the diamond sparkles. If the stone is cut too shallow, the majority of the lights will pass through it and escape through the pavilion. On the other hand, if the stone is too deep, there will be less sparkle and it will appear smaller than stones in the same carat weight.

The right depth for your diamond will also depend in part on the shape of the diamond.

Diamond Table %

To calculate the table percentage, you will need to take the diamond table facet and divide it by the total width of the diamond.

Keep in mind that you should never judge a diamond-cut quality based simply on the table percentage and the depth percentage. While they are both primary factors to consider when evaluating the diamond, it is important to note that they are not the only factors.

However, when you have two diamonds that have the same cut grade, you can use the depth percentage and the table percentage to refine the evaluation and to determine which of the two has the best light action.

Almost every diamond has a flat top. It is this topmost facet that is referred to as the diamond table. The table plays a huge role in the appearance of the diamond. One of its main functions is to refract the rays of light as they hit the diamond. It directs these rays to the other facets for maximum light action.

A well-cut diamond will appear sparkly because of this.

Keep in mind however that a large table is not always the best thing. When it is too big, the upper facets will simply not have the required space to disperse much light.

On the other hand, if the table is too small, very little light will be making its way inside the stone. As a result, the stone will not have much brilliance.

Of course, the ideal size of the table will depend on the size of the diamond. This is why jewelers will talk about table percentage.

But what is the ideal table percentage? This will depend on the shape of the diamond. When it comes to the round brilliant cut, for example, the ideal table percentage is from 54%-60%. For the emerald cut diamond, the ideal table percentage size is between 66% and 72%.

The difference might appear small but there is an effect on the stone.

Diamond Cut Grading

It is quite a daunting task when you want to evaluate the angles and shapes of the facets, the culet size, the symmetry, and polish and compare them to the overall performance of the diamond.

All these factors are looked at when a diamond is being graded. You can use the cut grade to determine the overall performance and quality of the stone. It simplifies the whole process of having to do this yourself and the great thing is that it is done by a professional gemologist.

While the cut grade is an important consideration when evaluating the stone, mostly when comparing two stones of the same cut grade will you compare the individual components, the symmetry, table%, depth%, and the polish.

That said, note that the ideal cut stone will refract back most of the light through the table and to the observer. Think of a hall of mirrors with you standing in the middle where you can see yourself in multiple reflections because the mirrors are at a perfect angle. If just one mirror is out of alignment, you will not be able to see yourself. The same concept applies to diamond facets.

How to determine the ideal depth and table percentage for your diamond

The table and the depth both have a big impact on the brilliance and sparkle of a diamond. The challenge comes in when trying to find the ideal depth percentage and table percentage of your stone.

It gets even more challenging when you have a limited budget to work with. One of the things that you have at your advantage is the fact that the depth and table can be measured in percentages. It doesn’t matter the size of the diamond; the percentages are constant.

This means that regardless of the size of the stone, it can still achieve an ideal depth and table size.

The chart below shoes the diamond depth % based on the shape of the diamond itself.

Diamond ShapeIdeal Excellent Very GoodGood
Round cut63-59.563.5-5964-5865-57.5
Princess cut75-6676.5-6478-6284.56
Asscher cut72-6076-5678-5480-50
Radiant cut75-6676.5-6478-6284-56
Cushion cut66-5572-5276-5078-46
Emerald cut72-6076-5678-5480-50
Marquise cut66-5672-5476-5278-46
Oval cut66-5672-5476-5278-46
Pear cut66-5672-5476-5278-46
Heart cut66-5472-5376-5278-46


The chart below shows table % based on the diamond shape

Diamond ShapeIdeal Excellent Very GoodGood
Round cut59-5460-5361-5263-52
Princess cut75-6677-6479-6282-55
Asscher cut72-6071-5576-5080-50
Radiant cut74-6476-6278-6082-55
Cushion cut64-5466-5268-5075-45
Emerald cut72-6076-5678-5480-50
Marquise cut64-5466-5268-5075-45
Oval cut64-5466-5268-5075-45
Pear cut64-5466-5268-5075-45
Heart cut64-5466-5268-5075-45


By understand a diamond’s ideal table percentage and depth percentage, you can now see how a diamond cut grade shows a well-proportioned diamond.

When you are out shopping for the perfect diamond, the eye can get attracted and then distracted by factors such as the clarity, the color and often the size of the stone. However, to judge the quality of the diamond, you need to understand the cut and the different proportions due to a different table and depth percentages.

What makes the diamond table so important is that it will allow the light into the stone while also dispersing it throughout the diamond. A diamond needs to have the right size for the table. It should be large to let in the lightest but not too large that light doesn’t refract inside the diamond.

When searching for the best diamond for you, you can use the above proportions to determine the cut and how ell light is dispersed inside the stone. you at also able to avoid stones that are not efficient at refracting light back to the observer.

The experienced cutter will aim to achieve three main things from a diamond.

The first is brilliance. This is the stone’s ability to both reflect and refract the light that gets into the diamond. While one of the main factors that affect the brilliance of the diamond is the number of facets, the table and depth are a major factor.

Second is the diamond’s scintillation. This is how the white and colored flashes appear when the diamond is moving and is also referred to as the sparkle. This is the life of the stone. The effect and amount of sparkle will depend on the refraction and reflection of light and these are directly related to the table percentage and the depth percentage.

The third is the diamond’s display of colored light. When the diamond is well cut, the observer can see visible colored light as the rays of light that enter the diamond are dispersed. A diamond with the ideal table and depth percentages will disperse white light into its seven visible colors resulting in stunning light action.

The diamond’s cut correlated directly to the table and depth. Sometimes the differences between two stones concerning brilliance and scintillation may not be noticeable by the naked eye. Always keep in mind that other factors will also affect the beauty of the stone and it is always important to check 360-degree videos and images to help you make the best choice.

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