Round Cut Diamonds

A round cut diamondThere are many different diamonds shapes. The most classic diamond shape however is the round cut diamond. It is the absolutely classic diamond with a somewhat timeless appeal.

Before going into the details of the round cut diamond I would like to encourage you to read through my educational material of the diamond 4Cs, that is: the cut, carat, clarity and color of a diamond. You have to have a basic understanding of the diamond 4Cs to understand the specifics of a round cut diamond.

Reasons to choose a round cut diamond

Most people buy round cut diamonds to set them on an engagement ring. By the way, it has not always been considered a universal way of proposing to give a diamond engagement ring to your future wife. In fact, we do have to thank the company De Beers for it. De Beers contributed to the diamond being seen as a universal symbol of love with a lot of ingenious marketing. I have written a separate post on De Beers marketing methods.

No matter what the reasons might be, it is a matter of fact that around 70 % of all diamond engagement rings consist of a round cut diamond. This might be either reason enough to follow the crowd or to choose another diamond shape on purpose to stand out among the crowd.

Check out James Allen for round cut diamonds. It is the only online store with high definition magnified 360° videos of all their diamonds in up to 40x magnification! This way you get to see exactly how the diamond sparkles and behaves in light. It currently also is the only store offering free return shippings in case you don’t like the diamond for whatever reason.
Inspecting a round cut diamond from all sides

So let’s have a look at why the round cut diamond is so popular:

For one thing the round cut diamond possesses a kind of universal appeal! The soothing round form with its associations of eternity will evoke neutral reactions at worst but very positive reactions at best. I have never heard anyone say that he or she considers a round cut diamond to be ugly.

I have heard people say however, that a heart-shaped diamond looks cheesy or that a marquise- or pear-shaped diamond looks sappy. Choosing a round cut diamond basically eradicates the risk of your girlfriend not liking the diamond shape you have chosen. Which is not to say that there are women who prefer other diamond shapes to the round cut diamond.

Ideal proportions in a round cut diamond provide the highest light return of all diamonds

Even more importantly though, an ideal round cut diamond provides for a maximum of light return compared to other diamond shapes. The specific proportions of a well-cut round diamond with its 57 facets allow for nearly 100 % light return.

You can see it quite easily if you compare the ASET images of a perfect round cut diamond and a perfect princess cut diamond. Although the princess cut diamond is the second most brilliant diamond shape you have much more areas of less intense light return (green) compared to a round cut diamond:

ASET image for round cut diamond and princess cut diamond in comparison

This means that round cut diamonds nearly reflect all the light that enters the diamond back to the viewer’s eye. Such a high percentage of light return is not possible with any other diamond shape! This is why a perfectly cut round diamond is the most brilliant diamond with the maximum amount of light dispersion compared to other diamond shapes.

Furthermore, the body color in a round cut diamond is the most difficult to make out. There are for instance diamond shapes that are more prone to showing off their body color because they trapping the light inside their body in a different manner.

For instance, usually you would not be able to tell the difference between a G and H colored diamond. If however you compare a G colored round cut diamond to an H color emerald cut diamond you will definitely be able to tell the difference.

Just have a look at this H colored emerald cut diamond and compare it to this G colored round cut diamond. Don`t you think that the perceived difference in body color is really astounding?!

Check out James Allen’s diamond color simulator if you want to be able to see what each color grade of a round cut diamond actually looks like:

James Allen diamond color simulator

Therefore round cut diamonds are the best suited diamonds to compromise on color. Thus, you get a bigger for your buck. In my post on diamond color I explain which color grade to choose for which ring metal to get the best bang for your buck.

What are the perfect proportions for an Excellent round cut diamond?

If you have decided to buy a round cut diamond you will want to choose a diamond which has the maximum amount of brilliance, fire and scintillation. For this to happen you will have to choose a diamond with the best proportions.

As you might know, the proportions of a diamand are graded within the “cut” of the 4Cs. The best cut grade is “Excellent” (graded by GIA) or “Ideal” (graded by AGS). My opinion is that you should never compromise on the diamond cut because it is the exact proportions of a diamond that determine how lively, bright and sparkly it will look! Furthermore you get an automatic boost in all the other 3Cs if you choose an “Excellent” cut.

Okay, but what if you have two diamonds with the same cut grade and you want to know which diamond will have a better light performance? This is when your knowledge about the perfect diamond proportions will come into play!

In 1919 the mathematician and renowned gemmologist Marcel Tolkowsky published his findings for the perfect diamond proportions in his thesis entitled “Diamond Design, A Study of the Reflection and Refraction of Light in a Diamond”. All diamonds that were within the parameters of the so-called Tolkowsky Ideal cut were considered to have an excellent light return.

The Tolkowsky Ideal Cut Proportions

Most recent research by the renowned gemmological grading institutes has found that round cut diamonds’ ideal proportions for maximum light performance are in fact somewhat close to the original Tolkowsky ideal cut. You can find the exact GIA proportions chart or AGS proportions chart here. The diamond below shows the commonly acknowledged proportions for an Excellent diamond.

Excellent proportions for a round cut diamond

Now, what if you have several diamonds that are lying within the above parameters? For sure, these diamonds will have a good light performance. But what if you want to find a diamond with an exceptionally good light performance? Then I would choose a diamond that lies within the proportions for super ideal cut diamonds below!

These parameters are even stricter than GIA’s or AGS’s criteria for an Excellent/Ideal cut and make sure that your diamond is only among the very best of all the Excellent/Ideal cuts out there:

Perfect diamond proportions for super ideal round cut diamonds

The easiest way to find super ideal cut diamonds is the following: Simply use this link for the pre-loaded set of parameters for super ideal cut diamonds. You can then adjust the other settings to fit your range of color, clarity, carat weight and price that you are interested in. Then open each diamond in a new tab, click on the icon of the grading lab and filter out all diamonds that do not meet the following criteria:

  • Crown angle between 34.0° – 35.0°
  • Pavilion angle between 40.6° – 41.0°
  • Culet: GIA “none” or AGS “pointed” (it is the same thing)
  • Polish / Symmetry: GIA Excellent or AGS Ideal

This way you can easily find a super ideal cut diamond for yourself! Indeed, I have found that round cut diamonds that lie within these parameters have a superb light performance. You should therefore always try to find a round cut diamond that lies within the above parameters.

Does your diamond have to be within super ideal proportions? It does not have to of course but if you really want a diamond with the best possible light performance you should go for super ideal cut proportions.

If you want to buy a diamond with super ideal proportions Brian Gavin and Whiteflash are an excellent choice! All of their signature diamonds are also hearts and arrows diamonds which are diamonds with the highest degree of symmetry.

Read my post on hearts and arrows diamonds if you want to know more about these specific diamonds.

The difference between a round cut diamond with super ideal proportions and one far outside super ideal proportions

Let’s see the difference between a well cut diamond and a diamond with worse proportions in moving action from all angles. Just compare these two diamonds to each other: This diamond is exactly within the proportions for super ideal cut diamonds and exhibits a lot of sparkle, brilliance and scintillation. You can see that the sparkle and fire are perfectly balanced.

This diamond outside the super ideal proportions on the other hand looks much less lively and exhibits considerably less sparkle and scintillation.

Obviously, the further you go outside these super ideal proportions the worse the light performance is gonna be! If you have several diamonds that fall within super ideal proportions it might be hard to distinguish the better one. You can always contact me in such a case and I will be more than glad to help you out!

How to go about finding a well performing round cut diamond?

Quite simply put: You should narrow down your choices to the three diamonds you like most. These three diamonds should not contain any poor performing diamonds. By this I mean to say that these three diamonds should have a really good optical performance.

In order to filter out all the poor performing diamonds there is a very usefool tool called the Holloway Cut Advisor. It is a great free tool to weed out low performing diamonds.

The Holloway Cut Adviser with the ScoreboardIt is a tool which was developed by Gary Holloway who has been active in the diamond industry since the early 70s. The Holloway Cut Advisor only works for round cut diamonds. In order to use the Holloway Cut tool you simply have to type in the parameters the tool is asking for and click “go”. You can find all of these parameters on your grading report. The Holloway Cut Advisor will then return a score ranging from 0 – 10 to you. The desired score has to be below the score 2.

The Holloway Cut Advisor asseses the light return, the fire, scintillation and spread of a diamond and gives a score for the Total Visual Performance of a diamond. Thus you can use this tool to narrow down your choices by weeding out any diamond that has a score above 2.

Please note however, that the Holloway Cut Advisor has its disadvantages and is only good for weeding out diamonds with a poor light performance. It should never be used to choose a diamond. Please read my post on the Holloway Cut Advisor Cons if you want to know more details. Please be aware that the Holloway Cut Advisor only takes into account the cut of a diamond. You still have to make sure that the clarity grade of your diamond is good enough to not take away any from its beauty.

Please note that if you buy a diamond within the proportions suggested for super ideal cut diamonds the diamond will always have a score below 2!

After having weeded out the low performing diamond you should have a specific look at the light performance of each diamond. In order to do so you should ask for the Idealscope image of each diamond. You can then compare the Idealscope images to each other and see which diamonds leaks the most light:

Idealscope image comparison between two diamonds

For instance, comparing the two diamonds above you can see that the diamond on the right has more white areas than the left diamond. I have circled these areas. As the white color indicates areas of white leakage, the diamond on the right has an overall worse light performance.Which means that the diamond on the right will not sparkle as brilliantly as the diamond on the left. But without the Idealscope images you would never know because both diamonds have very similiar proportions.

Read my article on Idealscope image evaluation if you want to know more details on how to analyse Idealscope images. By the way, online stores like James Allen, Brian Gavin and Whiteflash provide Idealscope images on all their diamonds. This is a rare service among online vendors. The biggest online vendor Blue Nile for instance does not provide any additional images. In fact it does not even provide any image of the diamond so that you are literally buying blindly!

Thus, no matter where you buy your diamond, you should never buy it without having had a thorough look at the Idealscope image first! Unless of course, you don’t care about the light performance of your diamond 🙂

I know that all of this stuff can be complicated for beginners. Thus, if you should have any question about round cut diamonds or if you feel stuck in your search, just write me a mail! I usually respond within 24 hours!

Round Cut Diamonds
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Sebastian Naturski loves to write about diamonds and share his knowledge with his readers.
When he is not working on his website he is studying law at Humboldt University of Berlin.
He has taken part in several international law competitions and likes to broaden his horizons.
His other big passion are languages. He is fluent in German, English, Polish and Japanese and got basic skills in French and Spanish as well.


  1. Hi Sebastian, your website is amazing and I have found all the information on it very helpful. Could you please tell me which of these 3 diamonds you would choose. All 3 have a HCA score under 2.

    Thanks for all your advice,

    • Thanks, Dave!

      I would choose the 3rd diamond as it has better cut proportions compared to the other two.

    • Hi Leo,

      Yes, you should! Even without the Idealscope analysis, the 360-degree image and the GIA report shows that the diamond is eye clean and bears an excellent cut. Those are the two most important indicators for an exquisite diamond. 🙂

    • Hi Keane,
      I truly think that this is a wonderful diamond. It is just nearly within the super excellent proportions as the pavilion angle is 42,2°. However, this is within GIA’s measuring tolerance and if you have not found a better diamond for your Budget I think that this one is a really good choice!

  2. Hi Sebastian.
    I just checked some round diamonds which I like with the Halloway Cut adviser. The score was above 2. Should I disregard these diamonds alone on this finding?

    • Hallo Hamolik,
      yes I am afraid you should do that! The Holloway is not a tool for choosing the right diamond but much rather a tool for weeding out the wrong diamonds.
      Only take diamonds into consideration that have a score below 2. And when you have these diamonds look at all the aspects like color and clarity and try to see which of these diamonds have the best proportions according to my table for super excellent round cut diamonds. Additionally also ask for an ASET/idealscope analysis from the customerservice.

  3. Hi Sebastian, I am now trying to find a diamond that fits your super excellent criteria. How exactly do I go about that?

    • Hi Brian,

      I would recommend to start looking for diamonds on a website where you can see magnified photos and high definition 360 ° videos of every diamond. This is really important to get a good feel of what your diamond will look like. The best website to do this at the moment right now is in my opinion.

      When browsing for diamonds make sure you only filter for the ones with the best cut which would be Ideal(Excellent) or True Heart. Click on all the stones that make a good first impression on you. Then click on the grading report on the left side of the diamond. It should be by either GIA or AGS. And then just have a look at the proportions. You will see all the crucial angles and heights of the particular diamond. Then just make sure that all of the important parameters are within the “Super Excellent Proportions” I have suggested in this post!

      Now, I won’t lie to you: This will take up some considerable time but it will surely pay off! This will most likely end up in you having a diamond with the best possible light performance! If you manage to find several stones like that which fit into your budget you can then select up to three stones and ask the customer service via the chat tool for an Idealscope of each diamond. This way you can also reserve all of these diamonds for you. After having received an Idealscope image you can then make the final decision and choose a truly superb diamond.

      If you should receive the Idealscope images and want my opinion on them you can always write me a mail!

      Cheers 🙂

  4. Great post. I particularly enjoyed jumping the post and reading about De Beers. I always wondered how the diamond engagement ring came into play. It was also interesting to learn about diamonds, in general, something that’s brand new territory for me.

    • Thanks Rico!

      Yeah, most people nowadays have difficulty believing that the “tradition” of the diamond engagement ring mostly came about through the decade-long advertising campaigns of De Beers.

      I think that it does not take away any of a diamond’s beauty but still it is important to know this fact. Especially in order to not be so easily susceptible to any kind of marketing influence regarding one’s budget for the engagement ring!

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