Diamonds 101
  • Cut grade represents the quality of a diamond's cut. Well-cut diamonds have optimal light return, adding to their sparkle.
  • Diamond shapes are sometimes referred to as 'cut styles', but here we're talking purely about a diamond's cut.
  • The ideal depth for an ‘excellent’ cut round brilliant diamond is somewhere between 59% - 63%.
  • The ideal table size for an ‘excellent’ round brilliant diamond is somewhere between 54% - 60%.
  • You can check the cut and proportions for your diamond by putting it into our free report service

Cut, not the place to cut corners...

Let’s start with the most pressing question, and get this dirty money business out of the way. How much should you spend on your perfect diamond? While there's a myriad of different answers to this, there is only one right answer: however freaking much you want. What you spend on your diamond is your own business. Our only advice on budget is to pick a price point and stick with it. Don't start looking at diamonds that are way above your financial cap; instead search for diamonds within that range that meet your criteria. Simple!

Deciding what criteria are most important to you is a little more nuanced and is a very personal choice. Some people want the absolute ideal quality diamond and are willing to go a bit smaller in size to get it. Others want to make sure Pam in accounting is desperately jealous and will go for the biggest carat weight stone they can afford, even if the color or clarity are slightly less than ideal. Both of these strategies, and everything in between, are perfectly acceptable.

However you prioritize the infamous 4 Cs is up to you; however, if you want to make absolutely certain you are getting the best bling for your buck, our advice is to pay special attention to ‘cut’.

What do we mean by diamond cut, and why is having a well cut diamond so important? Simply put, ‘cut’ refers to the proportions of the stone graded by the Gemological Institute of America (GIA).1. A well-cut diamond will enhance the brilliance (white light), fire (rainbow color light) and scintillation (sparkle 'flashes') of the stone. If you're going for a brilliant cut diamond such as a round brilliant, a princess cut, or a marquise cut, you'd expect it to be, well, brilliant. Even if you are going for a step cut like with an emerald cut or asscher cut stone, a well-cut stone can still help diminish the impact of inclusions and even make a yellowish stone appear whiter.

On the other hand, a poorly cut diamond can make it seem dull and lifeless - leaving Pam in accounting decidedly unimpressed. You might think that going for an ‘Excellent’ cut stone will negate any problems, but unfortunately it is not that simple. Let me explain using a simple example.

Let’s say you need $50. Pam from accounting produces two wallets and tells you that they both contain over $50 dollars. She also explains that although you may not open them, you can take whichever one you like and keep the money. Pretty straightforward.

Now let’s say that Pam leaves the room (typical Pam) and you get a chance to count the contents of each wallet. You discover that one wallet contains $51 dollars, while the other contains $251 dollars. The plot thickens! It is now quite obvious which wallet you should choose, but without the relevant details you could not have known this.

This same theory applies to diamond cut, because not all ‘excellent’ cuts are created equal. Indeed, two diamonds with a GIA triple excellent cut grade may perform in very different ways. The subtle differences in the proportions of each stone will completely change its interaction with the light.

Of course, if a stone is graded with a triple excellent grade from GIA, you can be pretty sure that the diamond is going to be beautiful. However, in order to truly understand the subtleties of diamond performance, you need to look beyond the GIA grading report. The best way to do this is to check the proportions of your stone against what is generally accepted as the ideal diamond proportions for round brilliant cut stones.

For rounds, aim for:

  • ‘Excellent’ Cut rather than a Very Good or Good cut
  • Table width percentage between 54%-60%
  • Depth percentage between 59%-63%
  • Crown angle between 33%-35%
  • Star length of 50%
  • Girdle of 2.5%-4%
  • Girdle thickness of thin to thick

For non-rounds, GIA does not grade a ‘Cut’ on its certificate. So leave that filter open when searching as it’s just values given by suppliers and retailers for GIA diamonds. You can also check out our Shape Guides for specific guidance on proportions.

GIA Anatomy of a Diamond


These parameters are helpful as they assist you in weeding out those underperforming diamonds. Even with an ‘excellent’ cut grade, your diamond may hide some secrets. For example, if the diamond is cut too deep (depth of 64% or more), the stone will look smaller face-up because all the weight will be hidden beneath the table. It will also lack the serious sparkle that ideal cut diamonds should have. An excellent cut diamond, if it has a pavilion angle of more than 41.25°, will have too much pavilion depth, causing light leakage beneath the table. The stone will then appear dull with poor light performance.

"Shopping online not only takes away all of that pressure, but is also allows you to take the journey on your own terms"

Once you have narrowed your choices down to three or four diamonds, you can then decide which other characteristics are important by comparing the other three C's. You might go for the diamond with the better color, or you might want to stick with better clarity; it's totally up to you. And remember, you can always ask a gemologist for their advice.

One note about shopping in a store vs. online. When you are in the store, it’s easy to get caught up in the fanfare of it all. What begins as quick window shopping can easily leave you $3,000 lighter - and you are not even sure what you bought. Shopping online can take away that kind of pressure, and allows you to take the journey on your own terms. You do the research, you compare the stones. And it’s not just about doing things at your own pace — purchasing online allows you to understand how the diamond will perform in what will be its natural environment.

Jewelry stores usually have a very sophisticated and carefully designed way of lighting their merchandise, showing their wares in the most flattering displays. The shopping experience may be enjoyable at first, but you might feel deceived when you see the diamond in ‘real’ light. Even the poorest cut diamonds can look great under the right lighting (kind of like Pam). Buying online let’s you think objectively between memorable, well cut diamonds and mediocre stones without any misleading lighting. The mediocre ones you can send back after all (online retailers listed here must offer 30 day back return guarantees).

Having tackled the complicated world of diamond cuts, our next post will focus on the other characteristics that determine the quality of your diamond. We will also take a deeper look into the weird world of diamond grading reports, so that you are equipped with all of the necessary information needed to buy your perfect diamond. Even you, Pam.

1. A Note on Symmetry: It is a common mistake to think that diamond cut and diamond symmetry are the same thing. In fact, they are quite different in that a diamond with perfect symmetry can still have a poor cut (like a steep pavilion discussed above). That said, an ‘excellent’ cut diamond will generally have ‘excellent’ or ‘very good’ symmetry (both are totally fine).

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