Diamond Cut

Diamond Cut


Diamond cut is one of the “four Cs” used to determine the overall quality, and therefore the price, of a diamond. Most diamond certificates will include a rating of the diamond’s cut, and, all other things being equal, a diamond with a better cut grade will command a higher price.

While the other three criteria (clarity, color, and carat weight) are relatively straightforward and simple enough that they can be understood and assessed by anyone, cut is a much more complex variable.

The methods for determining a diamond’s cut rating can vary depending on who is making the assessment, and, to further complicate the matter from the buyer’s perspective, some certificates don’t explain in much detail what criteria they used to grade a diamond’s cut.

That being said, if you’re thinking of buying a diamond, it would be well worth the time it takes to understand what different cut grades mean, how they’re determined, and what influence they have on a diamond’s price. This knowledge makes you better able to determine for yourself what a diamond’s price should be, distinguish a good deal from a bad one, and make the best possible investment when buying diamonds.

What is diamond cut?

In simple terms, the cut grade of a diamond refers to the “light performance” of a diamond, meaning the degree to which the diamond retains and reflects the light that enters it. A diamond with a good cut will be highly reflective and exhibit the best possible amount of sparkle. Conversely, diamonds that “leak” light through the bottom or side are usually cut too shallow or deep respectively, and they will thus have a less favourable cut grade.

Since it’s widely acknowledged that the aforementioned sparkle or brilliance is what gives diamonds their unique beauty, it follows that cut is what separates the most stunning diamonds from just ordinary ones.

It should be noted that “cut” in this sense does not refer to the intended shape of the diamond. If you’ve ever browsed for diamonds, you’ve probably come across terms like “Princess cut,” “Asscher cut,” “Emerald cut,” and so on. These refer only to stylized diamond shapes, and are not an indication of a cut rating.

What diamond cut grades are there?

At this point there still isn’t a standardized system for diamond cut grades. Each certifying authority uses its own system to rate the cut of a diamond, which can make things slightly confusing. Thankfully, however, the grades themselves are usually fairly self-explanatory, even if the methods used to determine them aren’t all that clear (more on that later).

Most certifiers use a five or six-point cut grading system. The typical system goes as follows, from best to worst:

  • Ideal: A diamond with maximum brilliance.
  • Premium: Nearly equal to Ideal.
  • Very Good: A diamond with slight light leakage.
  • Good: A diamond with decent reflectiveness, usually one which has been cut for size rather than brilliance.
  • Fair or Poor: Diamonds that reflect relatively little light.

Again, though, in some cases the terminology that is used can differ, the Gemological Institute of America, one of the major diamond rating authorities, for example, grades diamond cuts as Excellent, Very Good, Good, Fair, and Poor; so, diamond cuts rated “Excellent” by the GIA will be roughly equivalent to those rated “Ideal” by other bodies. Additionally, some diamond vendors have a special designation for their best cuts. For example, the online diamond retailer Blue Nile has a “Blue Nile Signature Ideal” cut, a term which they use to refer to cuts within the top 1%.

How are diamond cut grades assigned?

This is where things start to get complicated. The methods used to quantitatively assess the quality of a cut vary. The way the GIA determines what a diamond’s cut grade should be, for example, differs in very specific ways from the way other certifiers like the AGS do it. In most cases, these organizations don’t divulge the exact details of the processes they use.

The shape of a diamond also makes a difference with respect to how its cut grade is determined. Although there are some basic criteria that remain the same for any type of diamond, the exact methods used to grade a round diamond’s cut are different from those used to grade a heart-shaped diamond’s cut. The remainder of this explanation will focus on round diamonds, as this is by far the most common diamond shape.


One of the factors affecting the cut grade of a round diamond is the number of facets it has. Facets are the flat, defined areas on the surface of a diamond. The facets on round diamonds are usually triangular. Currently, it’s thought that the ideal round diamond should have 33 facets on the crown (the section of the diamond that sits above the girdle, which itself is the widest point of the diamond) and 25 on the pavilion (the lower, longer section of the diamond).

Diamond Cut

When there are imperfections on the surface of the diamond, cutters may add extra facets in order to obscure them. This results in a degradation in the overall quality of the cut.

While the facet count is generally agreed upon as a good way of judging the quality of a diamond cut, there are other points on which gemologists frequently disagree. Some of the other factors used by some authorities to help determine cut grades include the height of the diamond’s crown, the depth of the pavilion, the diameter of the table (the top of the crown), and the angles of the crown and pavilion.

The American Standard benchmark for round diamonds calls for a crown height of 16.2%, pavilion depth of 43.1%, and table diameter of 53% of the total girdle diameter. The Ideal Brilliant benchmark, however, calls for 19.2% crown height, 40% pavilion depth, and 56.5% table diameter. While these differences may be difficult for amateurs to discern, they are a good illustration of the difficulties associated with creating a simple assessment of a diamond’s cut.

Although there are some disagreements as to the exact proportions that constitute the perfect diamond cut, for prospective diamond buyers, the most important thing to understand is that diamond certifications provided by organizations like the AGS and GIA are trustworthy and meaningful. Reputable diamond vendors base the prices at which they buy and sell diamonds on the cut as well as the rest of the “four Cs.” When you purchase a diamond, you don’t have to worry about the perception of what makes a good diamond cut changing so much that the value of your diamond will be significantly affected.

Which diamond cut grade represents the best value?

Which sort of diamond is best for you largely depends on your budget. For buyers who are willing to purchase them, vendors usually recommend diamonds with the highest possible cut grades. However, this may be due to some self-interest on their part.

The other three Cs have an impact on diamond prices as well, so it can be difficult to gauge the exact difference in price between an Ideal or Excellent cut diamond and a Very Good cut. For casual buyers and budget-conscious investors alike, diamonds with a Very Good or Good cut grade can represent an excellent value. This is because, while they can be more affordable than otherwise equivalent Ideal or Excellent cut diamonds, the visible difference in quality is minimal.

At the same time, feel free to use your discretion. If, for example, you come across a diamond with an Ideal cut rating which has good ratings in the other categories and is still within your budget, then you should certainly consider it, as long as you’re dealing with a reputable vendor.

Picture notes

*1 – If you have some sort of diagram of a diamond that shows the different parts (table, crown, girdle, pavilion), that might be useful here.

Diamond Cut

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