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Quick answer: Cut is the most important grade for a lab grown diamond's sparkle. For round diamonds, choose the top cut grade on the report (Ideal or Excellent), with Excellent polish and symmetry. Fancy shapes like ovals and pears usually do not get an overall cut grade, so judge them by polish, symmetry, proportions and how they look in photos or video.
Cut is not the shape of a diamond; it is how well its facets are angled and finished to reflect light. Here is how to read cut grades and pick a stone that truly shines.
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Why Cut Matters Most
A diamond's sparkle comes from light entering the top, bouncing off the facets inside, and returning to your eye. When the angles are right, you see brightness, fire (flashes of color) and scintillation (sparkle as it moves). When a diamond is cut too deep or too shallow, light leaks out the bottom or sides, and the stone can look dull or dark even with top color and clarity.
Cut Grades on a Lab Grown Diamond Report
| Grade | What it means | Our advice |
|---|---|---|
| Ideal / Excellent | Top light performance and proportions | Choose this for rounds |
| Very Good | Slightly less light return | Fine for budget or small stones |
| Good | Noticeably less sparkle | Usually not recommended |
| Fair / Poor | Light leaks out; dull appearance | Avoid |
Grading labs use slightly different names for their top grades. What matters is choosing the highest cut grade the lab offers, not the exact word.
Cut Grade Scales by Lab
The two labs you will see most often on lab grown diamonds use similar but not identical words, so it helps to line them up.
| Lab | Cut grades for round brilliants, best to lowest | Note |
|---|---|---|
| IGI | Ideal, Excellent, Very Good, Good, Fair, Poor | Ideal is the top grade; Excellent is one step below it |
| GIA (natural diamonds and older lab grown reports) | Excellent, Very Good, Good, Fair, Poor | Excellent is the top grade |
| GIA (lab grown reports from October 1, 2025) | Premium or Standard tier | Finish is folded into one overall assessment |
So an IGI Ideal and a GIA Excellent both mean "top of the scale," but an IGI Excellent is not the same as a GIA Excellent. Our IGI vs GIA certificate guide covers the rest of the differences between the two reports.
The Parts of a Diamond That Cut Controls
A cut grade is a summary of several measurements working together. Knowing what each one does helps you read a report, especially for shapes that have no overall grade.
- Table. The large flat facet on top. A table that is too big can reduce fire; one that is too small can make the stone look smaller.
- Crown and crown angle. The upper part of the stone. Its angle shapes how much light splits into colorful fire.
- Pavilion and pavilion angle. The lower part. This is the mirror that sends light back up. If the angle is off, light escapes through the bottom.
- Girdle. The thin edge around the widest point. Too thin and it can chip; too thick and it adds hidden weight.
- Culet. The point at the bottom. Modern stones usually have none or a very small one.
For round brilliants, crown angles around 34 to 35 degrees paired with pavilion angles around 40.6 to 41 degrees are a classic combination for strong light return. The crown and pavilion have to be balanced with each other, which is why labs grade the whole set rather than any single number.
Polish and Symmetry
Every report also grades polish (how smooth the facet surfaces are) and symmetry (how precisely the facets line up). Aim for Excellent in both. Together with the cut grade, these are often called "triple excellent" for round diamonds.
How to Judge Fancy Shape Cuts
Ovals, pears, marquise, cushions, emeralds and radiants rarely receive an overall cut grade, because there is no single ideal set of proportions for them. Instead, check:
- Polish and symmetry: Excellent or Very Good.
- Bow tie: in ovals, pears and marquise, look for a light, faint bow tie rather than a dark band across the center.
- Length-to-width ratio: choose an outline you like; for ovals, 1.35 to 1.50 is popular.
- Depth: very deep stones look smaller for their weight; very shallow stones can look glassy.
- Real photos or video: the most honest check of sparkle.
Shown: Oval Lab Grown Diamond Solitaire Pendant with Four Prong Side Loops
Round Diamond Proportions at a Glance
If you like to check the numbers on a round brilliant, many top-performing stones fall roughly within these ranges. They are a guide, not a rule.
| Measurement | Typical strong range |
|---|---|
| Table | about 54% to 58% |
| Total depth | about 59% to 62.5% |
| Girdle | thin to medium, not extremely thick |
| Culet | none or pointed |
Common Cut Problems You Can Spot Yourself
You do not need a lab to notice a poorly cut stone. These issues show up clearly in a good photo or video.
Fisheye
A gray or white ring visible under the table. It happens when the pavilion is too shallow and the girdle reflects back through the top. It makes the stone look washed out.
Dark center (nailhead)
The middle of the stone looks dark because the pavilion is too deep and light leaks out the sides. Common in stones cut deep to keep extra weight.
Windowing
A see-through area in the center where you can read through the stone. Most common in shallow ovals, pears and cushions.
Strong bow tie
A dark band across the middle of ovals, pears and marquise. Almost all of these shapes show a faint bow tie, but a heavy one pulls attention away from the sparkle. Our oval ratio and bow tie guide shows what to look for.
Thick girdle
Adds weight without adding visible size. A stone with a very thick girdle can face up smaller than a better-cut stone of the same carat weight.
Popular Ratios for Fancy Shapes
For fancy shapes, outline is a matter of taste, but most buyers end up within these ranges. Use them as a starting point alongside polish, symmetry and real images.
| Shape | Popular length-to-width ratio | What to watch |
|---|---|---|
| Oval | about 1.35 to 1.50 | Bow tie strength |
| Pear | about 1.45 to 1.75 | Rounded shoulders and a centered point |
| Marquise | about 1.85 to 2.10 | Bow tie and matching ends |
| Emerald | about 1.30 to 1.50 | Even step facets and clean, open "hall of mirrors" look |
| Cushion | about 1.00 to 1.10 for square, higher for elongated | Facet pattern you prefer, from larger flashes to finer sparkle |
| Radiant | about 1.00 to 1.05 for square, 1.20 to 1.35 for rectangular | Depth, since radiants are often cut deep |
| Princess | about 1.00 to 1.05 | Protected corners in the setting |
If you are still choosing a shape, our guide to the best lab grown diamond shape for your budget compares how each one looks for its weight.
Is Cut Different for Lab Grown Diamonds?
No. Lab grown diamonds are cut and polished with the same tools and graded on the same standards as mined diamonds. The good news is that lower lab grown prices make it easier to afford a top cut grade without compromising elsewhere.
Cut vs Color vs Clarity: Where to Spend
Cut is the grade you see every time the diamond moves. Color and clarity differences between neighboring grades are often invisible once the stone is set, while a weak cut shows up as dullness right away. That is why we suggest a simple order: secure a top cut first, then choose color and clarity grades that look clean and white in your setting.
Moving up a cut grade usually costs less than moving up several color or clarity grades, and it changes the look of the stone more. A well-cut stone also faces up a little larger than a deep one of the same weight, so the cut grade can give you more visible size for your budget.
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Lab Grown vs Mined vs Moissanite: How Cut Shows
Lab grown and mined diamonds are the same material, carbon with a refractive index of about 2.42 and a hardness of 10, so the same angles produce the same sparkle in both. A top-cut lab grown diamond and a top-cut mined diamond look alike; telling them apart takes lab equipment.
Moissanite is silicon carbide, with a refractive index of about 2.65 and a hardness of about 9.25. It bends light more strongly than diamond, so it shows more colorful fire, sometimes described as a rainbow flash. Diamond's sparkle reads as brighter white light mixed with fire. Moissanite is not given a diamond cut grade by IGI or GIA. See our moissanite vs lab grown diamond vs diamond comparison for more.
How the Setting and Metal Work With the Cut
A great cut needs light, and the setting decides how much reaches the stone. An open prong setting, like a classic lab diamond solitaire ring, lets light in from the sides and shows off the cut fully. A bezel wraps the edge in metal; it protects the stone and still looks bright from the top, though it lets in a little less side light.
Two-stone designs such as toi et moi rings often pair different shapes, so match their cut quality as well as their size, or one stone will look livelier than the other.
Metal color does not change the cut, but it frames it. White settings in 925 sterling silver or white gold give a crisp, bright border. Yellow and rose gold in 10K to 18K add warmth around the stone, which many people love with a well-cut near colorless diamond.
Cut Quality in Small Stones
Earrings, tennis pieces and pave bands use many small stones, often called melee. These are not given individual cut grades, but cut still matters.
- Full cut vs single cut. A full cut round has the classic 57 or 58 facets. A single cut has far fewer, around 17 or 18, and gives larger, simpler flashes. Both are used in fine jewelry; full cut stones look more like small versions of a center diamond.
- Consistency. In a lab grown tennis chain, even cutting from stone to stone makes the line sparkle evenly. One dull stone stands out.
- Earrings. For lab diamond earrings with larger stones, match the cut quality of the pair as carefully as size and color.
Keeping a Well-Cut Diamond Sparkling
A lab grown diamond does not lose its sparkle, turn cloudy or change color over time. Its cut is permanent. What dulls it is a film of skin oil, lotion or soap on the pavilion, which blocks the light that the angles are designed to return.
Soak the piece in warm water with a little mild dish soap for a few minutes, brush gently behind the stone with a soft toothbrush, rinse and dry with a lint-free cloth. Check prongs now and then so the stone stays secure. Our jewelry care guide has more detail by metal.
Cut Mistakes to Avoid
- Choosing carat over cut. A larger stone with a poor cut can look smaller and duller than a well-cut smaller one.
- Assuming IGI Excellent is the top grade. On IGI reports, Ideal ranks above Excellent.
- Ignoring depth on fancy shapes. Very deep ovals and radiants hide weight; very shallow ones show windows.
- Judging from stock images. Only photos or video of the actual stone show its real light performance.
- Overlooking polish and symmetry. For fancy shapes these are the only finish grades you get, so they carry extra weight.
- Treating a cut grade as the whole story for fancy shapes. Two ovals with Excellent polish and symmetry can still differ in bow tie and brightness.
Step-by-Step: Choosing a Well-Cut Lab Grown Diamond
- Choose your shape and preferred outline or ratio.
- For rounds, filter to the lab's top cut grade (Ideal on IGI, Excellent on GIA) with Excellent polish and symmetry.
- For fancy shapes, filter to Excellent or Very Good polish and symmetry.
- Check table and depth against the ranges in this guide, and note girdle thickness.
- Watch a video of the actual stone for fisheye, dark centers, windows or a heavy bow tie.
- Compare millimeter measurements, not just carat weight, to judge face-up size.
- Choose a setting that lets light reach the stone and suits your lifestyle.
Who Should Prioritize Cut
Everyone buying a center stone should put cut first, because it decides how the diamond looks every day.
Buyers on a set budget benefit most, since a top cut lets you relax on color and clarity without losing sparkle.
Fancy shape lovers should spend extra time on photos and video, because there is no single cut grade to lean on.
Cut Quality at Ivevar
Surat, where our workshop is based, is one of the world's main diamond-cutting centers. We choose stones for how they perform in real light and handcraft each setting to show them off. Every piece ships free worldwide, with 30-day easy returns. Explore our lab grown diamond pendants and loose lab grown diamonds.
Shop Lab Grown Diamond Pendants
Oval Solitaire PendantShop Now
Princess Solitaire PendantShop Now
Emerald Cut Solitaire PendantShop Now
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Teardrop Halo Lariat NecklaceShop Now
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Frequently Asked Questions
Is Ideal cut better than Excellent?
It depends on the lab. On an IGI report, Ideal is the top cut grade and Excellent is one step below it. GIA's top grade is Excellent. Either way, choose the top grade the report offers.
Is Very Good cut acceptable?
For small stones or tight budgets, yes. For a center stone, we recommend the top cut grade whenever possible.
Why does my oval not have a cut grade?
Most labs do not give overall cut grades to fancy shapes. Use polish, symmetry, proportions and real images instead.
Can a better cut make a diamond look bigger?
Yes. A well-proportioned stone spreads its weight across the face-up area and looks brighter, which makes it look larger.
What does triple excellent mean?
It describes a round diamond with the top grade for cut, polish and symmetry. On an IGI report the top cut grade is Ideal, so you may see Ideal cut with Excellent polish and symmetry instead.
Does cut affect durability?
Yes, a little. A very thin girdle or sharp unprotected points, such as on a princess or marquise, are more likely to chip from a hard knock. A medium girdle and protective prongs or a V-tip on points reduce that risk.
Does GIA still give cut grades to lab grown diamonds?
For lab grown diamonds submitted since October 1, 2025, GIA issues a Premium or Standard tier that includes finish as part of the overall assessment, rather than a separate cut grade. Older GIA reports keep their original grades.
Does moissanite get a cut grade?
Not a diamond cut grade from IGI or GIA. Moissanite is a different gem, so judge its cut from photos, video and the seller's description.
The Bottom Line
Cut decides how your lab grown diamond sparkles. Choose the top cut grade for rounds, Excellent polish and symmetry for every shape, and trust real photos and video when judging fancy shapes.
Related Guides
- How to buy a lab grown diamond: a simple buying guide
- Diamond shapes guide
- Styling lab grown diamond pendants
Author Bio
Aumsri Pradhan
Founder, Ivevar Luxury
Aumsri Pradhan is the founder of Ivevar Luxury, a Surat-based fine jewelry brand that designs and handcrafts lab grown diamond and moissanite jewelry in its own workshop. She leads the brand's design and customer experience, from engagement rings and bridal sets to custom pieces made to each client's story. Through the Ivevar blog, she shares practical guidance on lab grown diamonds, moissanite, diamond grading and ring design to help buyers choose with confidence.
