By Gary A.
Edited by Brian M.
Published Sep 18, 2021
Edited on Oct 17, 2024
When it comes to maximizing brilliance, diamond proportion and ratio plays a crucial role in ensuring your stone sparkles at its best—are you ready to find out how this affects your engagement ring choice?
The way that a rough diamond is cut is by far the most significant factor behind its sparkle. Yes, it’s simple enough to learn the different shapes diamonds are cut into – and which cuts sparkle the most, and which ones you prefer – but, if you stop there, you’ll be overlooking the most important factor of all: proportion.
What do we mean by that? Well, two emerald cut diamonds can look totally different based on their proportions – despite the fact that they are both cut according to the same shape.
The same holds for round diamonds and fancy cut diamonds – even an eye clean, colorless diamond can be totally derailed by poor proportions, and appear pretty lifeless alongside one with ideal proportions.
Yes, it’s another complication, but one that you’ve got to go face-to-face with if you want to get the best possible diamond for your budget.
The ratios that exist between the diamond’s table, depth, and width, after it has been cut into the appropriate shape. These are represented in percentages, and used to determine the strength of a diamond’s cut, its value.
One of the biggest challenges diamond cutters face is determining how to create the biggest possible diamonds from an irregularly shaped rough stone – while also avoiding any major inclusions contained within it and, of course, ensuring good proportions.
A diamond’s value increases significantly with size, but getting the largest possible diamond out of the rough stone would typically mean creating a diamond with some very strange proportions. It may be far too deep, with a very long pavilion, or it may be too shallow, with a table percentage way too high to give a good sparkle.
Either way, the best approach is often the one that balances size with proportion. The biggest possible proportioned diamond will prove most popular among those looking to create beautiful diamond jewelry.
Very important. In fact, probably the most important thing to search for, alongside eye cleanliness.
Diamonds with excellent proportions will deliver better light performance – or, more specifically, better brilliance, fire, and scintillation. It is all too easy for a diamond to be cut too shallow or deep and, in both cases, this will mean that less light is able to take the optimal pathway through the diamond, and out of the table.
As a shopper, understanding the way each diamond’s proportions will impact its visual appeal is essential, through it’s a little more complicated than memorizing the color and clarity grades. You’ve got to know what percentages to look for, and which ones to avoid entirely.
Before we dive deeper into the specifics, here are some practical tips to help guide your decision-making process:
Now that you’ve got these practical tips, use Jeweler AI below to find the perfect engagement ring that suits your style and budget:
A GIA graded diamond with ‘Excellent’ or ‘Very Good’ proportions should be your focus during your search. The ‘right’ proportions depend entirely on the shape of the diamond, since what works perfectly for a Round cut diamond will look pretty bizarre on an Asscher or Emerald cut diamond. In any case, the perfect diamond proportions are those that maximize sparkle.
In a nutshell, good proportions will mean that a diamond is neither too shallow nor too deep, and neither too wide nor too narrow. Its structure will support its beauty, rather than obstructing it.
These ideal proportions will comprise depth and table percentages, the culet (lowest point), the girdle (where the crown meets the pavilion), and height to length ratio. Below, we will list the ideal cut diamond proportions for each diamond but, for now, we will look in closer detail at the ideal diamond cut proportions for the Round cut diamond, and for the Emerald cut diamond – two totally different shapes – to give you a good idea of the different proportions required to maximize sparkle.
The ideal proportions for realising the full sparkle potential of a Round Brilliant cut diamond is as follows…
Excellent | Very Good | |
Length to Width Ratio | 1.00 – 1.009 | 1.01 – 1.019 |
Table | 56% – 59.9% | 54% – 55.9% Or 60% – 60.9% |
Depth | 59% – 62.3% | 585 – 58.9% Or 62.4% – 63.5% |
Culet | None | Very Small |
Girdle | Thin to Slightly Thick | Very Thin to Slightly Thick |
Excellent | Very Good | |
Length to Width Ratio | 1.35 – 1.44 | 1.30 – 1.34 Or 1.45 – 1.50 |
Table | 60% – 65.9% | 58% – 59.9% Or 66% – 72.9% |
Depth | 63% – 67.9% | 59% – 62.9% Or 68% – 69.9% |
Culet | None | Very Small |
Girdle | Very Thin to Slightly Thick | Very Thin to Thick |
Here, you can see that the table of an Emerald diamond with ideal cut proportions will cover more of the diamond’s width than the table of a Round diamond, also with ideal cut proportions.
The same is true of the Oval. The best diamond measurements will be very different than they are for a Round cut. This shape also features an elongated silhouette and has very different requirements for Length and Width ratio, depth, and table than a Round Brilliant.
Below, we have put together the ideal proportions (graded ‘Excellent’ by the GIA) for each diamond cut, so that you can approach your chosen shape with the right information at your side.
Remember, however, that an experienced jeweler will be incredibly well-versed in this subject, and won’t steer you in the wrong direction. They understand the importance sparkle holds for engagement rings better than anyone, so don’t panic about learning these numbers by heart.
Length to Width Ratio | Table | Depth | Culet | Girdle | |
Asscher | 1.00 – 1.029 | 60% – 65.9% | 63% – 67.9% | None | Very Thinto Slightly Thick |
Cushion | 1.00 – 1.029 | 60% – 65.9% | 63% – 67.9% | None | Very Thinto Slightly Thick |
Cushion (Rectangle) | 1.18 – 1.28 | 60% – 66.9% | 63% – 67.9% | None | Very Thinor Slightly Thick |
Emerald | 1.35 – 1.44 | 60% – 65.9% | 63% – 67.9% | None | Very Thin to Slightly Thick |
Marquise | 1.90 – 2.00 | 53% – 65.9% | 58% – 62.9% | None | Very Thinto Slightly Thick |
Oval | 1.35 – 1.42 | 55% – 62.9% | 58% – 62.9% | None | Very Thinto Slightly Thick |
Pear | 1.55 – 1.62 | 53% – 62.9% | 58% – 62.9% | None | Very Thinto Slightly Thick |
Princess | 1.00 – 1.029 | 67% – 72.9% | 67% – 72.9% | None | Very Thinor Slightly Thick |
Radiant (Square) | 1.00 – 1.029 | 61% – 69.9% | 61% – 67.9% | None | Very Thinor Slightly Thick |
Radiant (Rectangle) | 1.22 – 1.32 | 60% – 66.9% | 63% – 67.9% | None | Very Thinor Slightly Thick |
Round | 1.00 – 1.009 | 56% – 59.9% | 59% – 62.3% | None | Thin to Slightly Thick |
The wrong dimensions can undermine a diamond’s light performance, and turn an otherwise beautiful stone into something not worth your time.
Again, as we’ve said, it’s not like you’ve got to get these tables memorized. Your jeweler isn’t going to ask you to recite them like you’re back in kindergarten.
Even so, it’s massively helpful for you to go into the process of understanding the basics of diamond proportion, and why it is so important to anyone looking to buy the best possible diamond for their bride-to-be.
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