The Complete Round Cut Diamonds Guide

When we think of an engagement ring, one image comes to mind: a sparkly round cut diamond! This shape is the vanilla of engagement rings, but it’s never bland, it has always reigned supreme.

Round Cut Diamonds

Some would try to be edgy and opt for fancy shapes; little do they know that the magic behind the round diamond lies in its cut proportions. So, don’t be fooled by its basic form because it can exhibit a bright and fiery sparkle that no other diamond shape can ever imitate.

Now, before diving deep into the details of the round cut, I encourage you to read my posts on the Diamond 4Cs: cutcolor, carat, and clarity. These pages will serve as your prelude/refresher to better understand the nature of round cut diamonds. If there’s no need for an intro, let’s get started!


Why Choose Round Cut?


1. Round Cut Diamonds Are Universal

 

The round cut diamond hasn’t always been the universal choice for engagement rings. In fact, we have the De Beers commercial to thank for it! With their ingenious marketing, the diamond is now seen as the universal symbol of love.

(I have written a separate post on De Beers’ marketing methods if you’re intrigued by this backstory.)

James Allen Round Cut Diamonds

Today, 70% of all diamond engagement rings consist of round cuts. The calming round form with its association with eternity evokes neutral reactions at worst, but very positive responses at best. I have never heard anyone say that he or she considers a round cut diamond to be unappealing.

On that premise, choosing a round cut diamond eradicates the risk of your lady not liking the diamond shape you have selected. Although, it’s not meant to be just a safe bet – it is a sure win!


2. Round Cut Diamonds Exhibit Supreme Light Performance

 

More importantly, ideal round cut diamonds provide a maximum light return compared to other shapes. The proportions of a well-cut round with its 57 facets allow for nearly 100 % light return.

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


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


This means that round cut diamonds reflect virtually all the light that enters back to the viewer’s eye. Such a high percentage of brilliance is not possible with any other diamond shape! This is why a perfectly cut round diamond has the most amount of fire and scintillation compared to other cuts.


3. Round Cut Diamonds Show the Least Amount of Body Color

 

Round Cut Diamonds on finger

The body color in a round cut is the most difficult to make out. For instance, there are diamond shapes that are more prone to showing off body color as they tend to trap light in a different manner.

Usually, you would not be able to tell the difference between a G and an H color. But if you would compare this H-colored emerald cut diamond to this G-colored round cut, you will definitely be able to spot the color variation. Don’t you think that the perceived difference in body color is astounding?


James Allen Color SimulatorCheck out James Allen’s diamond color simulator if you want to see what each color grade of round cuts actually looks like:


That said, round cut diamonds are the best-suited diamonds to compromise on color and get a bigger bang for your buck!

(In my post on diamond color, I explain which color grade to choose for each  ring metal to help you maximize your budget.)


What are the Ideal Proportions for a Round Excellent Cut Diamond?


If you have decided to buy a round cut diamond, you would want to choose one that has the maximum amount of brilliance, fire, and scintillation. For this to happen, you must opt for a diamond with the best proportions. As you might know, the proportions are graded within the “cut” of the 4Cs.


The Diamond 4Cs

The best cut grade is “Excellent” (graded by GIA) or “Ideal” (graded by AGS). In my opinion, you should never compromise on the diamond cut because it is the exact dimensions 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 one will have a better light performance? This is when your knowledge of cut proportions comes into play!


The Tolkowsky Ideal Cut

In 1919, the mathematician and renowned gemologist, 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 prominent gemological grading institutes has found that the round cut diamonds’ ideal proportions for maximum light performance are somewhat close to the original Tolkowsky Ideal Cut. (You can find the exact GIA proportions chart or AGS proportions chart here.)


Excellent proportions for a round cut diamond

 

The table on the left shows the commonly acknowledged cut proportions for an Excellent Cut.

These dimensions guarantee that your round diamond bears exquisite brilliance, fire, and scintillation.

 


Super Ideal Round Cut Diamonds

Now, what if you have several diamonds that are cut within the parameters above? For sure, these diamonds will have a good light performance.

But what if you want to find a diamond with an exceptional sparkle? Then, you would have to pick a one that lies within the proportions of a super ideal cut! These parameters are even stricter than GIA or AGS’ criteria for an Excellent/Ideal cut. It guarantees that your diamond is among the very best!

Proportions for super ideal cut diamonds


The Easiest Way to Find Super Ideal Cut Diamonds:

 

Round Cut Diamonds Online Shopping

Simply use this link for the pre-loaded set of parameters for super ideal cut diamonds. You may adjust the other settings to fit the 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 super ideal cuts by yourself! If you’re already sold, Brian Gavin and Whiteflash are excellent choices. All of their signature diamonds are also Hearts and Arrows which are diamonds with the highest degree of symmetry.

(Know more about hearts and arrows on this page.)


What’s the Difference Between an Excellent Cut and a Poor Cut?


Let’s see the difference between a well-cut diamond and one with bad proportions from all angles. Just compare these two diamonds to each other: 

0.90 CARAT G-VS2 EXCELLENT CUT ROUND DIAMOND

0.90 CARAT G-VS2 EXCELLENT CUT

0.90 CARAT G-VS2 GOOD CUT ROUND DIAMOND

0.90 CARAT G-VS2 GOOD CUT

 

The diamond on the left is within super ideal cut proportions and exhibits a lot of dispersion and scintillation. You can see that the sparkle and fire are pretty balanced. The diamond on the right, however, is outside the super ideal proportions and has considerably less sparkle.

Naturally, the further you go outside super ideal dimensions, the worse the light performance is going to be! If you have several diamonds that fall within these standards, it might be hard to choose “the one.” You can always contact me in such a case, and I will be more than glad to help you out.


How to Find a Well-Performing Round Cut Diamond


1. Filter with the Holloway Cut Advisor Tool

Simply put: Narrow down your choices to the three diamonds you like most. Your selection shouldn't contain any poor performing diamond. Meaning, they should have superb optical performance.

In order to filter out all the poor performing gems, there is a very useful (and free!) tool called the Holloway Cut Advisor (HCA):

The Holloway Cut Advisor with the Scoreboard

The HCA was developed by Gary Holloway who has been active in the diamond industry since the early 70s. To use the Holloway Cut tool, you would have to type in your diamond's parameters and click “go.” It will then return a score ranging from 0 – 10 to you. The desired score has to be below 2!

This tool assesses the light return and spread of a diamond and gives a Total Visual Performance score. Thus, you can use it to weed out any diamond that has a rating above 2.


Holloway Cut Advisor results

 

Please note, however, that the Holloway Cut Advisor is only good for getting rid of diamonds with a weak light performance. It’s merely a rejection tool and should never be used as a selection tool.

(Read my take on the Holloway Cut Advisor Cons if you want to know more details.)

Also, please be aware that the HCA only takes into account the cut of a diamond. You still have to make sure that the clarity grade is good enough. Now, it goes without saying that if you buy a diamond within the super ideal proportions, your diamond will automatically have a score below 2!


2. Check the Ideal Scope Images

After weeding out low-performing diamonds, you should have a specific look at light performance. For you to do so, compare their Ideal Scope images and see which diamond leaks the most light:

Idealscope image comparison between two diamonds

With the two diamonds above, you can see that the one on the right has more white areas than the left diamond. White color indicates areas of white leakage which mean that the diamond on the right will not sparkle as brilliantly as the diamond on the left. But without the Ideal Scope images, you would never know because both diamonds have very similar proportions.

(Read my article on Ideal Scope image evaluation if you want to know more!)


3. Never Buy Round Cut Diamonds Blindly

 

Buying Diamonds Blindly

Online stores like James AllenBrian Gavin, and Whiteflash offer Ideal Scope images for all their diamonds. This is a rare service and even the biggest online vendor Blue Nile, doesn’t provide any additional images – so you are literally buying blindly!

Take note that wherever you may shop, you should never purchase a diamond without having a thorough look at its Ideal Scope image. Unless of course, you don’t care about light performance.


James Allen Round Cut Diamonds Collection

Another thing to look out for are high definition magnified 360° videos in up to 40x magnification! This way you get to see exactly how the diamond behaves in light. James Allen does that and is currently the only shop offering free return shipping in case you didn’t like the diamond for whatever reason.


The Takeaway


Round Cut Diamonds Engagement Ring

The round cut is deemed as the favorite because it’s the Godfather of engagement rings. Its popularity goes a long way, beyond its classic form. Whether you are into minimal style, a trend-follower, or a technical shopper, round cut diamonds fit the bill.


Should you have any questions about round cut diamonds, or if you feel stuck in your search, comment below or just write me a mail! I usually respond within 24 hours. 🙂

 

The Complete Round Cut Diamonds Guide
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About 

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.

18 Comments

  1. Hi,

    Thank you for great reading and info! This diamond fits into your “Super Ideal” table but only scores 2.4 when I check the tool you linked to?? Should I not consider it? I know it is strong fluorescence but I can look at it IRL so I will check if it is ok in that regard. HRD: 160000005170
    https://my.hrdantwerp.com/
    Thank you!

    • Hi John,

      Most, if not all, diamonds within super ideal cut proportions score below 2. To confirm if your diamond proportions are legit, make sure it is reviewed by a reputable lab such as GIA and AGS. Then again, the Holloway Cut Advisor is only good for getting rid of diamonds with a weak light performance. It’s merely a rejection tool and should never be used as a selection tool.

      • I am puzzled because a diamond I am interested in purchasing is ranked “GIA Excellent” according to Holloway cut advisor but the HCA ranking is a 3.7. How is that possible? The Depth is 61.4, the Table is 59%, the Crown Angle is 35.5 and the Pavilion Angle is 40.9. The cut grade and holloway cut advisor conflict each other. What should I do? I am confused and frustrated.

        • Hi Nina,

          The HCA tool is only used for weeding out diamonds and not as a selection tool. You can simply base on cut proportions and if your diamond is within the parameters, then you’ll get a brilliant diamond. A table of 59% is a bit big, but everything else is within standard round cut proportions.

    • Hi Ali,

      Try to look for a table size of 53% to 58% – this is the ideal range. Too big of a table creates a reflection that takes away from the brilliance of the diamond. Also, inspect the diamond’s real images and make sure it is eye clean if you’re opting for a SI1 clarity. Medium fluorescence is okay for I-colored diamonds. But see for yourself whether through pictures or in person. Do not buy blindly. Good luck!

  2. 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.
    https://www.jamesallen.com/loose-diamonds/round-cut/2.21-carat-j-color-vvs2-clarity-excellent-cut-sku-2659393

    https://www.jamesallen.com/loose-diamonds/round-cut/2.01-carat-j-color-if-clarity-excellent-cut-sku-2878221

    https://www.jamesallen.com/loose-diamonds/round-cut/2.00-carat-i-color-vs1-clarity-excellent-cut-sku-2850291

    Thanks for all your advice,
    Dave

    • 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!

  3. 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.

  4. 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 jamesallen.com 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 🙂

  5. 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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