Diamond Buying Advice: What are the best ideal proportions for cushion cut diamonds?

By Todd Gray

March 11, 2014

Video of Brian Gavin Signature Cushion Cut Diamond Review, AGSL 104066516010Dear Todd, I’m happy to have found your site. My husband proposed with a lovely half carat Lucida diamond ring from Tiffany & Co., which seemed like the best diamond available at the time. However the more I read about diamonds, the less confident I feel about Tiffany’s and our future choice should we choose to upgrade for an anniversary. I’d like to learn more about the cushion cut diamonds offered by James Allen & other web sites.  I’d appreciate your advice on selecting the best cushion cut diamond, something around 1.4 – 1.7 carats depending on price. Thanks – Veronika G.

Thank you for your inquiry Veronika. I believe that a lot of people experience difficulty when trying to shop for cushion cut diamonds online because of the broad range of production standards used to produce cushion cut diamonds, which make it practically impossible to select cushion cut diamonds “by the numbers” with any degree of consistency outside the production standards of specific brands.

Ideal Proportions for Cushion Cut Diamonds

The first challenge that people face when trying to compare cushion cut diamonds online, is that the term “cushion cut” is used to describe any diamond which is square or rectangular in shape and which is cut to have a pillow-like outline.

The article which I wrote to to announce the debut of the Brian Gavin Signature Cushion cut diamond featured a reference chart that features the more common cushion cut diamond facet structures that are found in the market, each of which has the potential to create different types of sparkle because of how they produce flashes of light which can differ dramatically in terms of size and intensity… combine the variety of facet designs for cushion cut diamonds with a broad range of proportions, and it becomes practically impossible to predict the volume of light return and what the balance of brilliance and dispersion is likely to be.

Why practically every cushion cut diamond is a different shape:

Upon receipt of your request, I conducted a search for cushion cut diamonds on James Allen and limited the search to diamonds with an overall cut grade of either GIA Excellent or AGS Ideal, as you can see there is a broad range of shapes for the cushion cut diamonds offered by James Allen:

Best ideal proportions photographic examples of cushion cut diamonds from James Allen

Although several of the cushion diamond diamonds presented above by James Allen share the same facet design, each one of them appears to exhibit a different level of contrast and disperses light through the stone somewhat differently. In addition since the diamonds are graded by the GIA Laboratory, there is no indication of the crown or pavilion angle measurements and thus the only measurements we can use to form an opinion of the diamonds is the total depth, table diameter, and girdle thickness… that’s like buying a car online without knowing whether it has a four, six, or eight cylinder engine.

The good news is that James Allen does provide us with a video of the diamond, which enables us to get an idea of the actual shape of the diamond, as well as get an idea of how light travels through the diamond, and the levels of contrast being exhibited by the diamond. However James Allen does not readily provide images of the cushion cut diamonds which they represent as seen through the various reflector scopes that we use to judge optical symmetry and estimate the levels of light return… they might consider providing them upon request.

Brian Gavin Signature Cushion versus the Brellia Cut Diamond:

If you’re a regular reader of my diamond blog, then you know that I’m a big fan of the Brian Gavin Signature Cushion cut diamond. One of the things which I love about the cushion cut diamonds produced by Brian Gavin, is that he designed his cushion modified brilliant to rival the visual performance of the round brilliant super ideal cut diamonds that he produces, it even warrants an overall cut grade of AGS Ideal-0 from the AGS Laboratory, which is practically unheard of.

Brellia cushion cut diamond reviews, example of the girdle edgeThe only other ideal cushion cut diamond that I’m aware of is the Brellia Diamond. However the Brellia Diamond features a girdle edge which can vary from thin to extremely thick, as is evident in their promotional video. I highlighted the upper and lower peaks of the girdle edge of the Brellia Diamond pictured to the left with red arrows to make it easier for you to identify. I’m personally not a fan of diamonds that vary dramatically in girdle thickness, because in my experience it has the potential to create a window into the side of the diamond, reduce light return, make the diamond difficult to set, and cause the diamonds to loosen in the setting more than a uniform girdle edge.


One of the things which I discussed with Brian Gavin during the development phase of the Brian Gavin Signature Cushion cut diamond, was his desire that the design of the diamond feature a girdle edge which was consistent. Creating a uniform girdle edge on a cushion modified brilliant cut diamond turned out to be quite a challenge, but eventually Brian Gavin discovered how to do it without sacrificing diamond cut quality.

GIA Excellent vs AGS Ideal-0 Cushion Cut Diamonds:

GIA Excellent versus AGS Ideal Cushion Cut Diamonds, James Allen 5151787692 The majority of “top quality” cushion cut diamonds that you find in the market will be graded by the GIA with Excellent Polish and Symmetry, however this does not represent an overall cut grade of GIA Excellent because the GIA does not issue proportions grades for fancy shape diamonds. Thus this 1.70 carat, H-color, VS-2 clarity, cushion cut diamond from James Allen is not a “GIA Excellent Cushion Cut Diamond” because there is no such thing… it merely has a polish and symmetry grade of GIA Excellent. Notice how the proportions diagram for the cushion cut diamond referenced to the left provides only the measurements for total depth and table diameter, there is no indication of the crown or pavilion measurements because the GIA does not provide this information for fancy shape diamonds; the report format offered by the AGSL provides these measurements.

One of the problems I faced as a diamond buyer, is that cushion cut diamonds tend to be cut from diamond rough that couldn’t be used to manufacture any other popular diamond shape, except perhaps a princess cut diamond. This is because the diamond rough used to produce cushion cut diamonds is irregular in shape, and this lack of consistency in the shape of the diamond crystal means that every cushion cut diamond produced from this type of diamond rough will be different in shape, which results in a facet structure which is extremely inconsistent.


The lack of consistency which is part of the nature of cushion cut diamonds, makes it extremely difficult to select cushion and princess cut diamonds with confidence from suppliers which have production standards that I am not familiar with.

When I was actively employed as the diamond buyer for Nice Ice, I used to purchase GIA Excellent graded cushion cut diamonds from only two companies, both of which were the authorized distributors for the production of one diamond company which specialized in the production of cushion cut diamonds. Their cushion cut diamonds were absolutely amazing, unfortunately the company went out of business in 2008. Despite making every effort to do so, I was never able to find another reliable source for cushion cut diamonds of the diamond cut quality that I am accustomed to.

Therefore I was very excited when Brian Gavin told me that he was in the process of developing a cushion modified brilliant cut diamond which was designed to rival the light performance and sparkle factor of round brilliant ideal cut diamonds, and I got to see several of the prototypes during the design and production process… it was an amazing experience and I can say with confidence that the Brian Gavin Signature Cushion cut diamond is one of my favorite diamond shapes.

Brian Gavin Signature Cushion Diamond Prices:

If you are not familiar with the cost of ideal cut diamonds and attempt to compare them with diamonds of less precise quality, you might believe that Brian Gavin Signature Cushion cut diamonds cost more than cushion cut diamonds with the same characteristics.

However keep in mind that a Signature Cushion cut diamond from Brian Gavin is one of the few cushion cut diamonds available that has an overall cut grade of AGS Ideal-0 and which is graded on the Platinum Light Performance grading platform, which uses Angular Spectrum Evaluation Technology (ASET) to measure the diamonds for brightness and determine where in the room the diamond is gathering light from. I don’t know the percentage of cushion cut diamonds that are capable of demonstrating this level of outstanding optical precision, but fewer than 1% of round brilliant cut diamonds qualify for the overall cut grade of AGS Ideal-0 on the Light Performance grading platform!

And keep in mind that there is no way to determine the proportions of cushion cut diamonds graded by the GIA Laboratory without additional computerized proportions analysis, because the GIA does not provide measurements for the crown and pavilion sections of a diamond on their diamond grading reports… the only factors which we know to be Excellent are the Polish and Symmetry grades, and the symmetry grade refers to “meet point symmetry” and not “optical symmetry” which simply means that the facet junctions come together relatively well at the points where they meet.

If you want a diamond that performs exceptionally well in a variety of lighting conditions, and which exhibits a high amount of contrast, which is what enables eyes to perceive depth and see beauty in a diamond, you need a diamond which is cut to a high level of optical symmetry, and the only way to verify that is to examine the diamond using various reflector scopes which are designed for that purpose. Brian Gavin provides images of his diamonds as seen through these scopes on the diamond details pages for every diamond in his inventory, so that his clients can rest assured that every diamond they purchase from BGD is cut to the highest standards.

It can take up to four times longer to cut and polish a diamond to this level of precision, and every Brian Gavin Signature Cushion cut diamond is cut from the same type of diamond rough which is used to produce the Brian Gavin Signature round diamonds, which enables the cutters to manufacture a cushion cut diamond which is symmetrical in shape and consistent in facet structure. The symmetrical shape and facet design result in an even distribution of light throughout the diamond, and a virtual balance of brilliance (white sparkle) and dispersion (colored sparkle) with a high degree of scintillation (sparkle created while the diamond is moving).

I suppose that a good analogy for the difference in the quality of diamond rough used to produce the Brian Gavin Signature Cushion cut diamond and other cushion modified brilliant cut diamonds, would be to imagine that you are having your kitchen remodeled and trying to decide between having custom cabinets made by a master craftsman who is going to use the finest quality of wood available, personally selecting each piece of wood to ensure that it meets his standards for quality, and then carefully crafting each junction point so that it flows perfectly into the next, so that there are no gaps and seams where light can sneak through or create an unsightly gap; versus buying some cabinets from the local box store which are prefabricated to fit a variety of kitchens, and which may or may not fit well in your actual kitchen, but with no way of knowing until they are slapped together.

Brian Gavin Signature Cushion Recommendations:

I realize that you indicated that you would like to consider diamonds weighing between 1.40 – 1.70 carats, however there are very few diamonds produced in the 1.40 – 1.49 carat range because of the weight increase which occurs between the 1.49 – 1.50 carat marks; the reality is that the diamond cutters are better off using the same piece of diamond rough to produce a diamond of virtually any cut quality that weighs more than 1.50 carats.

There are several Brian Gavin Signature Cushion cut diamonds available just over the 1.50 carat mark, but I kind of feel that if you’re going to pay the premium that occurs at the 1.50 carat mark, that it would be nice to really benefit from the premium by jumping up just a little bit more in carat weight. The 1.678 carat, G-color, VS-2 clarity, Brian Gavin Signature Cushion cut diamond which is featured in the video located at the top of this article offers a good middle ground in terms of color and clarity, it will face up bright white and provides a clarity which will be eye clean. As you can see by the lab report pictured to the left, the diamond has an overall cut grade of AGS Ideal-0 and the ASET scan reveals that it is nice and bright.

You can search Brian Gavin for Signature Cushion cut diamonds to see what else is available within the price range which you designated, and I am happy to help you consider all of the options which are available, however I don’t know the range of color and clarity that you prefer… Let me know a little more about what you’re looking for and I’ll see what I can find for you to consider.

Todd Gray

About the author

A mad scientist with a passion for improving diamond cut quality to maximize light performance and sparkle factor. I speak geek in degrees of optical precision between bouts of freediving. My ghostwritten ramblings haunt the rabbit holes of information found on many diamond vendor sites. Diamond buyer, author, consultant, errant seeker of deep blue water.

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  1. Would you be able to compare to GIA certificates for cushion cuts and inform me which one would be a better purchase?

    1. Hello Pallavi,

      Please email me the GIA diamond grading report numbers (I don’t need the actual reports, just the numbers) and I will look up the details and try to help you determine which one of the cushion cut diamonds is the best option.

      As a matter of fact, it is practically impossible to predict the light performance of a fancy shape diamond by the numbers. However, hopefully, I’ll be able to find some images of the diamonds within the multiple listing service that we use to trade diamonds globally and be able to provide you with a better assessment. Email me at diamonds(insert @ symbol)niceice.com

      Thank you.

      — Todd

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