When most people think about diamonds, they focus on size or clarity. Makes sense — big, clear diamonds sound impressive. But honestly, there’s something way more important if you want real sparkle and beauty: the cut.
Now, a lot of folks mix up “cut” with “shape.” Shape just means round, oval, pear, whatever. Cut is totally different. It’s about the skill and precision in how a diamond is crafted — the angles, the symmetry, the way everything lines up so light hits the stone, dances inside it, and bounces right back out. That’s what gives a diamond its fire.
This is why you can line up two diamonds with the same carat, colour, and clarity, and they’ll look nothing alike. One might burst with sparkle and catch your eye from across the room. The other? Just kind of sits there. It might look great on paper, but in real life, it falls flat.
In our main guide, The 4 Cs of Diamonds, we lay out why cut matters most. Here, we’re digging deeper. We’ll explain what those cut grades actually mean, how grading really works, and why “Excellent” or “Very Good” aren’t always the whole story.
By the time you’re done reading, you’ll see why cut needs to be your number one when you’re choosing a diamond — whether you’re leaning natural or lab-grown. Plus, you’ll know how to skip the hype and avoid paying extra for a diamond that just doesn’t shine.
“Diamond cut controls how light enters, reflects, and creates sparkle.”
Diamond Cut Grades Explained: Why They Matter
Diamond Cut vs Diamond Shape — They Are Not the Same Thing
A lot of people mix up diamond cut and diamond shape. It sounds like they’re the same thing, but they’re not — and getting them confused can end up costing you.
Diamond shape is all about the outline of the stone. Think round, oval, pear, cushion, emerald — those are shapes. It’s really a style choice. Shape changes the look of the ring, not how much the diamond sparkles.
Cut’s a different story. Cut is about how well the diamond’s actually crafted. We’re talking angles, proportions, symmetry, polish — all the stuff that decides how the light bounces inside the stone. That’s what gives a diamond its fire.
Here’s the thing: any diamond shape looks flat and lifeless if the cut isn’t right. But with a great cut, even a simple shape can look amazing.
That’s also why only round brilliant diamonds get an official cut grade, like Excellent or Very Good. The other shapes don’t have one set system, so you have to judge them by their proportions and how they handle light.
We go deeper into this in Popular Engagement Ring Shapes & Their Meaning, where we show how style and performance overlap.
Knowing the difference between cut and shape puts you way ahead of most buyers. It helps you pick a diamond that looks stunning — not just pretty on the outside, but truly brilliant.
“Shape affects style. Cut controls sparkle.”
Diamond Cut Grades Explained: Why They Matter
Why Cut Is the Most Important of the 4 Cs
If you remember just one thing from this guide, let it be this: the cut matters most when it comes to how a diamond actually looks. It beats carat, colour, or clarity every time.
You can find a big diamond that’s almost flawless and barely has any colour, but if the cut’s bad, it’ll still look lifeless. The magic—those flashes and sparkles—doesn’t come from size or purity. It’s all about how the light bounces inside the stone.
A well-cut diamond grabs light from the top, bounces it around inside, and shoots it right back out at you. That’s what gives you all that brilliance (the white sparkle), fire (those bursts of colour), and scintillation (the way it seems to dance and twinkle when you move it).
But get the cut wrong, and the light just escapes out the sides or bottom. Suddenly, the diamond looks tired and dull.
That’s why two diamonds with the same carat, colour, and clarity might look completely different in real life. One glows—bright, sharp, full of life. The other? Flat, dark, glassy. Even if both come with great certificates, you’ll feel the difference the moment you see them.
Our main guide, The 4 Cs of Diamonds, spells it out: always put cut first. You can let colour or clarity slide a little if you need to save money, but cutting corners on cut? You’ll almost always wish you hadn’t.
It doesn’t matter if you’re picking a natural diamond or something lab-grown. The right cut is what makes a diamond come alive.
“Same grades on paper. Completely different sparkle in real life.”
4. How Cut Affects Light Return (Why Some Diamonds Sparkle and Others Don’t)
A diamond’s sparkle isn’t some kind of magic trick. It’s all about physics. Every diamond has one main job: grab the light, toss it around inside, and shoot it back out the top. When a diamond does this right, it looks lively and sparkles like crazy. When it doesn’t, even the priciest diamond just looks flat and dull.
Now, the cut is what makes or breaks that sparkle.
Too shallow? Light goes in, slips out the bottom, and you end up with a stone that looks watery and glassy. Hardly any sparkle.
Too deep? The light gets lost inside, leaks out the sides, and suddenly your diamond looks dark and smaller than it really is.
But when you get the cut just right, with perfect angles and proportions, the magic happens. Light bounces around inside and bursts out the top in sparks of white and flashes of colour. That’s why a well-cut diamond can actually look brighter than a bigger one, seem whiter than its official colour grade, and just feel more dazzling overall.
In The 4 Cs of Diamonds, we always say: start with the cut, not the carat. What your eye cares about most is how the diamond plays with light. Once you get how light return works, it’s easy to see why cut is the most important thing.
“Only an ideal cut returns light to your eye — creating sparkle.”
Diamond Cut Grades Explained: Why They Matter
Diamond Cut Grades Explained (What “Excellent” Really Means)
When you start looking at diamonds side by side, you’ll notice grades like Excellent, Very Good, or Good on their reports. These labels are supposed to tell you how the diamond will perform, but honestly, they don’t always give you the full picture.
If you’re checking out round brilliant diamonds, labs like GIA and IGI actually give them a cut grade. Other shapes don’t get one simple grade for cut, which is why people often stick with round diamonds when they want guaranteed sparkle.
So, what do these cut grades really mean?
✔️ Excellent (GIA) / Ideal (IGI)
This is the top of the line. We always recommend going for this grade, especially for engagement rings. Diamonds with this cut have the right proportions to really bring out their brilliance, fire, and that eye-catching sparkle. But even here, not every Excellent cut looks exactly the same. Tiny tweaks in the angles or proportions can make a difference in how the diamond shines in real life.
✔️ Very Good
These diamonds reflect most of the light and still look gorgeous, but they don’t quite have the same sharp sparkle as the Excellent grade. If you look closely and pick carefully, Very Good cuts can be a nice way to balance looks and budget.
✔️ Good, Fair & Poor
Diamonds in this range lose a lot of light. They usually end up looking dull, dark in the centre, or just sort of lifeless, even if they weigh more carats. For engagement rings, we say skip these grades altogether.
In our main guide, The 4 Cs of Diamonds, we break down why cut should always come first—more than size or clarity. The cut is really where a diamond’s personality shows up.
“Not all cut grades perform the same — even within the same category.”
Diamond Cut Grades Explained: Why They Matter
Ideal vs Super Ideal Cuts — Is There Really a Difference?
When you dive into diamond shopping, you’ll probably run into terms like “Ideal Cut” and “Super Ideal Cut.” They sound fancy, right? But what do they really mean, and are they actually worth the extra money?
An Ideal Cut diamond fits into a pretty strict set of proportions that are all about getting the most sparkle. We’re talking about the right balance between table size, depth, crown angle, and pavilion angle. Most diamonds graded as Excellent by GIA or Ideal by IGI already hit this level, and they look seriously brilliant.
Then there’s the Super Ideal Cut. This is where cutters get even pickier — these diamonds follow even tighter rules, sometimes going beyond the usual grading standards. You end up with a diamond that throws off slightly sharper sparkles, sends back more light, and has flashes of fire that really pop, especially under bright lights.
But honestly, here’s the thing: To the naked eye, the difference between Ideal and Super Ideal is tiny. Most people won’t spot it without a side-by-side comparison and special lighting.
If you’re shopping for a diamond, an Excellent or Ideal cut will already give you amazing sparkle and value. Super Ideal cuts are really for the die-hard diamond fans or those who just want the absolute best, no matter the cost.
When we talk about the 4 Cs of Diamonds, the smart move is to go for a great cut first. After that, balance out colour and clarity. Only after you get those right should you think about paying extra for ultra-precise cutting.
At the end of the day, especially for an engagement ring, it’s not about ticking every box on a grading report. What matters most is how the diamond looks every single day on your hand.
“Super Ideal cuts offer marginal gains — but Ideal cuts already deliver exceptional sparkle.”
Diamond Cut Grades Explained: Why They Matter
Why Poorly Cut Diamonds Exist (And Why They’re Still Sold)
People ask us all the time: “If cut matters so much, why are there so many badly cut diamonds out there?”
Honestly, it all comes down to money. Cutting for weight brings in more profit than cutting for beauty. When it’s time to shape a diamond, cutters face a choice. They can carve it just right for maximum sparkle, or they can leave a little extra weight, bump up the carat number, and charge more. Carat weight drives up price, so some diamonds end up too deep or too shallow—just to keep that scale tipping higher. Sure, the certificate looks impressive, but in real life? Not so much.
Poorly cut diamonds tend to stash weight at the bottom, so they look smaller than their carat size would suggest. Sometimes the centre looks dark. Sometimes they just don’t shine at all—no fire, no brilliance.
Yet, these diamonds still sell. Most people pay attention to carat, colour, or clarity first, not realizing cut is the first thing their eye actually notices.
In our guide The 4 Cs of Diamonds, we explain why it’s smarter to pick a slightly smaller diamond with an Excellent cut, instead of a bigger one with a bad cut. The well-cut stone will always look brighter, whiter, and way more dazzling.
Once you know why poorly cut diamonds are out there, you can avoid overpaying—and find a diamond that truly stands out.
“Extra weight hidden below the surface reduces sparkle — but increases price on paper.”
Diamond Cut Grades Explained: Why They Matter
What You Can Actually SEE Between Cut Grades
On paper, the gap between cut grades looks tiny. In person, though, it’s usually the first thing you notice.
Put two diamonds side by side in normal lighting—anyone can spot the difference, no training needed.
✔️ Excellent / Ideal Cut
These diamonds shine all the way to the edge. You get bold white sparkle, sharp flashes, and they still look lively even in dim light. They often look a bit bigger and cleaner than you’d expect for their grade. Honestly, this is the level most people fall for right away.
✔️ Very Good Cut
Very Good cut diamonds still sparkle well, but the light isn’t quite as crisp. Sometimes you notice small dark patches or a little less fire when they move. If you check carefully, these can work, especially if you need to watch your budget—but they just don’t have that instant wow that Excellent cuts bring.
✔️ Good, Fair & Poor Cuts
Now the difference really jumps out. Diamonds at this level often look:
- darker in the middle,
- kind of glassy or flat,
- less lively,
- dull, especially under indoor lights.
Even folks with zero jewellery experience usually spot it right away.
That’s why the cut always comes first. Out of all the 4 Cs, cut is the one your eyes pick up on immediately—way before you even think about size or clarity.
“Cut grade is the one difference most people can see immediately.”
Diamond Cut Grades Explained: Why They Matter
How to Choose the Right Cut Grade (Without Overthinking It)
So, you’ve figured out that cut really makes a diamond sparkle. Naturally, you’re probably wondering, “Alright, which cut grade should I actually pick?”
Here’s the good news: it’s pretty straightforward for most people. If you want a diamond that turns heads and looks lively in everyday light, aim for an Excellent cut (if you’re looking at GIA) or Ideal (if you’re looking at IGI). That’s the sweet spot—sparkle, value, and sheer wow factor all in one. Honestly, this is what we suggest for almost every engagement ring.
Now, if you’re working with a tighter budget, don’t stress. A Very Good cut can still look great—as long as you check it out carefully, either in person or on video. Watch out for dark patches or areas that look dull. This is where having someone with experience really helps.
But don’t go lower than Very Good. Once you get into Good, Fair, or Poor territory, the diamond just loses its magic. You can add carat weight, sure, but it won’t hide the lack of sparkle.
Our main guide on The 4 Cs of Diamonds goes into this in more detail, but here’s the bottom line: it’s usually smarter to pick a slightly smaller diamond with an excellent cut than a bigger one that’s just kind of meh. Your eyes always notice sparkle first.
Thinking about lab-grown diamonds? Great—here’s another bonus. Higher cut grades are a lot easier to find without blowing your budget, so you really get the best of both worlds.
“When cut is right, the diamond does the talking.”
Cut Is Where Diamonds Come Alive
If there’s one thing you should take away from this guide, it’s simple: diamond cut matters most. Sure, carat weight looks impressive on paper. Colour and clarity sound good when you see them on a certificate. But the cut? That’s where the magic happens. The sparkle that catches your eye and makes you fall in love with a diamond — that’s all about the cut.
Once you understand cut grades, shopping for a diamond gets a lot easier. You won’t waste money on dull stones, and you’ll know exactly where to put your budget. When you get the cut right, everything else starts to make sense.
Want the full story on how cut fits into the world of diamonds? Check out our main guide: The 4 Cs of Diamonds: The Complete 2025 Guide.
If you’re picking out an engagement ring, we’ve got more guides to help you dive deeper:
How to Choose the Perfect Engagement Ring in 2025
Lab-Grown vs Natural Diamonds: The Complete 2025 Guide
Popular Engagement Ring Shapes & Their Meaning
At Blackwell Jewellers, we don’t just rely on certificates. We hand-select every diamond for real-world beauty and performance. Whether you’re looking at natural or lab-grown stones, we’ll help you find one that truly shines.
“When cut is right, the diamond does the talking.”
