When it comes to choosing a diamond, cut is arguably the most important factor—and sometimes the most misunderstood. Many people hear “cut” and think of shape (like round or oval), but in gemology, diamond cut refers to how well a diamond’s proportions, symmetry, and polish work together to reflect light. And that has a direct impact on how sparkly, bright, and lively the diamond looks.
This all being said, a diamond’s cut can make or break its appearance. Even a diamond with excellent color and clarity can look dull if it’s poorly cut. On the other hand, a well-cut diamond can outshine stones with higher grades in other areas.
In this guide, we’ll walk you through what diamond cut really means, how it’s graded, and why it plays such a big role in a diamond’s beauty. We’ll also share what to keep in mind when comparing stones side by side, so you can find something that doesn’t just look good on paper, but something that truly lights up in person.
What Is Diamond Cut?
Diamond cut refers to how well a diamond has been shaped and faceted to reflect and refract light. How well a diamond is cut depends on its proportion, symmetry, and the way each facet (surface of the diamond) interacts with light.
A well-cut diamond will return more light to your eye, giving off that hallmark sparkle we associate with fine jewelry.
When a diamond is cut too shallow or too deep, light escapes from the sides or bottom, making the stone appear darker or dull. But with ideal proportions, the diamond acts like a mirror, catching and returning light back to the viewer’s eyes.
Cut is the only one of the 4Cs that’s directly influenced by human craftsmanship. It takes precision, expertise, and intention to unlock a diamond’s full visual potential.
How Diamond Cut Is Graded
The Gemological Institute of America (GIA) has come up with a globally recognized system for grading the cut of a diamond.
The GIA cut grade is based on a few different criterion:
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Brilliance: This is the amount of white light reflected back to the viewer
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Fire: This is the colorful flashes of light created as light disperses through the diamond
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Scintillation: This is the sparkle that is given off when the diamond is viewed dynamically.
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Proportions: How the diamond’s depth, table, and angles relate to one another
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Polish & Symmetry: The smoothness of the facets and the precision of their alignment
Based on these factors, diamonds are graded on the following scale:
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Excellent: Offers maximum brilliance, fire, and scintillation. Reflects nearly all the light that enters the diamond.
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Very Good: Very bright, with only minor visual differences when compared to Excellent cuts.
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Good: Decent light performance but less sparkle overall; some light may escape.
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Fair: Noticeably reduced brilliance and scintillation due to poor proportions.
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Poor: Significant light leakage. Little sparkle or visual appeal.
An important point of this grading system is that it only applies to round brilliant diamonds - the most brilliant and popular shape of all. Fancy shapes—such as cushion, pear, and emerald—do not have an official GIA cut grade. Because of this, assessing the cut quality of fancy-shaped diamonds often requires an in-person evaluation or guidance from a trusted expert.
Cut vs. Shape: What’s the Difference?
As a quick note, shape refers to the outline of the diamond—round, oval, princess, pear, etc.—while cut refers to how well the diamond’s facets are arranged and proportioned.
Round brilliant cuts are the only shape with formal GIA cut grades. Other shapes (sometimes called “fancy shapes”) don’t have the same grading consistency, which makes shopping for them a little more nuanced. That’s where having an expert eye comes in handy—especially for shapes like emerald or Asscher cuts that don’t reflect light as brilliantly as rounds, but still rely on symmetry and polish to shine at their best.
Why Cut Matters More Than You Might Think
Of all the 4Cs, cut has the biggest impact on a diamond’s visual performance. That’s because even a diamond with flawless clarity and color will appear lackluster if it doesn’t return light effectively. On the flip side, a slightly lower color or clarity grade can be masked by an excellent cut—especially in well-lit environments.
A great cut can also make a diamond appear larger than it really is. That’s because it reflects more light from edge to edge, creating the illusion of greater spread. For buyers trying to maximize the look of their diamond without jumping in carat size, this is a huge win.
Cut also influences how color shows up. A well-cut stone will reflect so much light that it can help downplay a faint yellow tint—especially in the near-colorless ranges of the color scale. This is another reason why cut is often prioritized above the other Cs when balancing overall quality.
Practical Tips When Evaluating Diamond Cut
When evaluating diamond cut, it’s best to stick to Excellent or Very Good grades for round brilliant diamonds, as these offer the strongest light performance—meaning more brilliance, fire, and sparkle.
Round diamonds are the only shape with an official GIA cut grade, making them easier to assess objectively. For fancy shapes—like oval, pear, marquise, cushion, or emerald cuts—there’s no standardized cut grade, so it’s especially important to compare stones side by side. Pay close attention to brightness, symmetry, and how well the sparkle carries from edge to edge.
Another thing to mention, given the popularity of carat, it would be wise to think twice before sacrificing cut quality in favor of carat weight. A larger diamond with a poor cut may appear dull or lifeless, lacking the lively sparkle that gives diamonds their allure. In fact, if you’re trying to stretch your budget, prioritizing cut is often the smartest move—an excellent-cut SI1 or SI2 diamond can easily outperform a higher-clarity, heavier stone with a mediocre cut when viewed in person.
Ultimately, cut is the most influential factor when it comes to a diamond’s visual beauty. Even the most flawless diamond won’t shine without a great cut. If sparkle is what you’re after—and it almost always is—cut is where you’ll get the most visible impact for your investment.
We’re Here to Help
At Paul’s Jewelers, we’ve been helping clients in Milwaukee and beyond choose exceptional diamonds for over 55 years. Whether you’re shopping for a special pendant, necklace, or custom engagement ring, we’re here to make the process clear, supportive, and tailored to you.
Our in-house team of gemologists and jewelers can walk you through the details—showing you how cut affects not just a diamond’s technical grade, but how it truly looks in person. We’ll help you compare stones, explain what makes one sparkle more than another, and guide you toward a piece that shines in every way.
Stop by our showroom and experience the expertise and service that has made us Milwaukee’s preferred jeweler for over 5 decades.
