Diamond Cut Grading: Everything You Need to Know About Quality

If you’re out there looking for the best diamond for your money, then please contact us and let us know your budget and what you’re looking for. We’ll sift through thousands of diamonds online and send you suggested stones to choose from that fit your needs the best.

Bottom Line Recommendation

If you are buying a round diamond, limit your selections to “Excellent” cut diamonds (if graded by GIA) or “Ideal” cut diamonds (if graded by AGS). If you are buying any other shape diamond, it is essential that you see a high quality image of the diamond before deciding to buy as fancy shape cut quality cannot be deciphered using certificate stats alone. Because of this, we recommend you stick with Blue Nile or James Allen.

As always, if you are unsure about any aspect of the process, please feel free to contact us with your questions.

What is a “Diamond Cut”?

Diamond Cut refers to how well proportioned a diamond is. For example, what percentage of a diamond’s diameter is its depth? What are its various angles and how do they interact with one another? While these may seem like esoteric questions, these are the essential factors that determine how beautiful your diamond will be.

Differences in Diamond Cut greatly impact sparkle, aesthetic appeal and value of a diamond.

The factors affecting the price of a diamond include:

  • Proportions (table, width, depth)
  • Symmetrical facets (the mirrors, windows and steps of a diamond)
  • Brilliance (brightness of white light reflection)
  • Fire (dispersion of colored light)
  • Scintillation (the flashes of sparkle when light moves)
  • Finishing details (permanent treatment and polishing)

To further understand the factors impacting Diamond Cut quality, let’s examine a diamond’s proportions, primarily its table, width and depth. These elements are universally measured and are excellent indicators of a diamond’s cut quality.

Diamond Measurements

About Diamond Table

Diamond table % is determined by dividing the width of the table (top surface area) by the width (diameter) of the diamond. For example, if the table facet is 3.5mm wide, and the diamond is 5mm wide, the table % is 70%.

If the table percentage is too large, light won’t reflect off of the diamond’s crown angles and facets. Vibrant reflections of color won’t be seen as the light will escape from the top of the diamond instead of reaching the eye.

If the table percentage is too low, light will remain trapped inside the diamond and be emitted through other parts of the diamond instead of to the eye.

The ideal table % depends heavily on the Diamond Shape. If you’re unsure of an excellent table % for your diamond, please
contact us
and we will walk you through the options and factors.

About Diamond Width

A diamond’s width is determined by measuring from one end of its girdle (the diameter at its widest point) to the other end of the girdle.

The width is most important when it comes to determining length to width ratio, which signifies how proportionate the diamond is along with its intended shape (i.e. square vs. rectangular).

Length to width ratio is measured by dividing the length of the diamond by the width. For example, if a diamond has a length of 5mm and a width of 3mm, the length to width ratio is 1.67.

About Diamond Depth

Depth % refers to the height of the diamond, from the culet to the top of the table. Depth is measured in millimeters and percentage. By dividing the depth by the width, the depth % is achieved.

As an example, if a diamond is 4mm in depth and 4.5 mm in width, the depth percentage is 88.8%.

In most cases, a lower depth % of two equal carat diamonds will appear larger due to the increased width. On the other hand, a depth % that is too low can create a darker appearance as it will not reflect light as powerfully.

What’s the difference between Diamond Cut and Diamond Shape?

The terms Diamond Cut and Diamond Shape have distinct meanings.

Diamond Shape describes the outline or figure of the diamond. For example, Pear Shaped and Round Brilliant refer to the shape appearance of the diamond.

Cut refers to the facets, symmetry, dimensions and reflective qualities of the diamond. A Heart Shaped Diamond, for instance, may be cut shallow or deep, dull or brilliant. The Heart Shape remains, while the Cut may differ significantly. The finer the cut, the greater the brilliance and fire of the diamond.

Diamond Cut Proportions

Diamond Cut Proportions directly affect a diamond’s ability to reflect light and provide brilliance. Proportions are based on the ratios between size, angle and shape of each diamond facet. Various combinations of these elements impact how the diamond will interact with light, which determines its overall beauty and lasting appeal (as well as its GSI grading).

How Light reflects through a diamond

What happens when a Diamond Cut is too shallow?

When a Diamond Cut is too shallow, light hits the pavillion at a low angle. The light travels through the diamond and exits through the sides, instead of reflecting through the table and to your eyes.

While shallow cut diamonds may seem large based on their table size, the escape of light at the bottom significantly reduces the diamond’s brilliance, sparkle and fire.

What happens when a Diamond Cut is too deep?

When a diamond is cut too deep, light hits the pavilion at a sharper angle, causing it to immediately reflect to another pavilion. The light is forced to retract and pass through the bottom of the diamond. As this happens, light is dulled and the diamond becomes less vibrant and radiant.

A Diamond Cut that is too deep also tends to look smaller than those of an ideal cut.

What is the best cut for a Diamond?

Simply put, a well cut diamond maximizes the light that strikes each pavilion. Instead of escaping through other parts of the diamond, light reflects back through the crown and table.

When it comes to determining the highest grade possible, GIA uses the term “excellent” while AGS (the inventory of the cut grade) uses the word “ideal.” These cuts are well proportioned with optimal facet angles, allowing the brilliance and fire to pass through the table for all to see.

For these reasons, excellent cuts are more valuable and more luminous. When buyers have a budget, we often advise choosing a smaller, well cut diamond as opposed to a larger carat that is poorly cut.

If you’re unsure of an ideal cut for your diamond, speak to an expert to walk you through the process.

How GIA Grades Diamond Cuts

The GIA (Gemological Institute of America) is a renowned and well-respected diamond grading entity that issues reports for diamonds.

As an independent entity, GIA does not have a financial stake in the sale of the diamond. When you are in the market for diamonds, it’s advisable to seek a GIA certificate to view the Diamond’s Cut grade.

The following scale is how GIA claims to grade Diamond Cut. Unfortunately our experience has been that this is far from reality:

Excellent Excellent Cut Diamonds provide the highest level of fire and brilliance. Because almost all of the incoming light is reflected through the table, the diamond radiates with magnificent sparkle.
Very Good Very Good Cut Diamonds offer exceptional brilliance and fire. A large majority of the entering light reflects through the diamond’s table. To the naked eye, Very Good diamonds provide similar sparkle to those of Excellent grade.
Good Good Cut Diamonds showcase brilliance and sparkle, with much of the light reflecting through the table to the viewer’s eye. These diamonds provide beauty at a lower price point.
Fair Fair Cut Diamonds offer little brilliance, as light easily exits through the bottom and sides of the diamond. Diamonds of a Fair Cut may be a satisfactory choice for smaller carats and those acting as side stones.
Poor Poor Cut Diamonds yield nearly no sparkle, brilliance or fire. Entering light escapes from the sides and bottom of the diamond.

The reality is that 55% of all round diamonds receive an excellent cut grade. Even with excellent cut grades, about 25-30% of these “excellent” diamonds are rejected when our consultants search for diamonds due to bad specs (depth, table and angles).

To make sure you don’t end up with a mediocre excellent cut, contact us and one of our consultants will guide you through the process.

Factors for Determining Diamond Cut Quality

Because Diamond Cut is an enormous element in determining the beauty and brilliance of any diamond, there are some complexities.

The main factors impacting Diamond Cut Quality are:

  • Proportions: the ratios and sizes of the diamond’s depth, width and table
  • Symmetry: precision of the facets, mirrors, windows and steps
  • Polish: the shine and glow of the diamond surface

When you’re looking to see how well cut a diamond is, take note of how its facets and angles reflect light. Specifically, note how bright and sparkly the light return is when placed under a normal lamp.

You’ll want to gauge the diamond’s fire (the rainbow light of reflection) and its brilliance (colorless light and sparkle of the diamond). Be sure to also watch for any dark spots within the piece.

When a diamond is poorly cut (even if it has a high Color or Clarity grade), light will not reflect as well back to your eyes, making it a duller, more lifeless diamond.

Be sure to review the GIA cut grade on a diamond’s report, which will include ratings of Poor, Good, Very Good or Excellent.

How Cut Grade Affects Price

The precision and quality of a Diamond’s Cut, namely its proportions and symmetry, greatly impact a diamond’s beauty and price.

If the facets (the glossy flat surfaces of a diamond) are proportional, for instance, they will refract and reflect light back to the eye in tremendous fashion. Diamonds that are not as precisely cut will have facets and pavilions that do not refract and reflect light as spectacularly.

The amount of light return and brilliance found in an exceptionally cut diamond is worth the extra cost. Without brilliance and fire, a diamond is less than radiant — no matter the Carat weight or table size.

Spending more on a diamond’s Cut rather than its Color or Clarity will significantly impact the beauty of your diamond.

For example, these True Hearts Cut Round Diamonds make for exquisite engagement rings because they are the best Cut that James Allen offers in Round Cut diamonds. Even though they cost a bit more than Excellent Cut diamonds in the same Color and Clarity, their brilliance far exceeds the others. In other words, they’re worth the price. The added brilliance and luminosity offered by such ideal cuts make all the difference in how the diamond appears and interacts with light.

As another example, Brian Gavin offers a Signature collection called Hearts & Arrows which includes some of the best Cut diamonds on the market. For example, this 1 Carat Diamond has tremendous brilliance at an excellent price point.

If you are working within a budget, we recommend forgoing a GIA grade in Color and Clarity to ensure you are selecting an ideal cut diamond.

Our Recommendations For Buying The Right Diamond

When it comes to selecting an ideal diamond, we recommend a quality Diamond Cut over anything else. For GIA Certified Diamonds, we recommend choosing an Excellent cut grade. For AGS Certified Diamonds, choose an Ideal cut. When we search for a diamond, we filter more heavily on Cut. You can see our parameters by looking at this James Allen diamond search.

For Maximum Brilliance: Consider a Brian Gavin Signature cut. Brian is a leading industry expert in the field of cut optimization. His Signature cuts are on par with the famed Hearts on Fire brand—only far cheaper.

For Round Brilliant Cut Diamonds, don’t give any credence to an online vendor’s cut grade. Only focus on the GIA or AGS cut grade on the certificate.

In addition to reviewing a GIA or other grading report, be sure to look at the diamond yourself or have an expert assist you. Most importantly, ensure the diamond is appealing to you and your personal style and desires.

Our primary focus is making sure your diamond search is easy, simple and accurate. We want you to find the highest quality diamond while staying within your budget.

If you’d like assistance with finding and selecting a diamond, we’ll be happy to filter through the cuts and make recommendations for you.


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