Diamond Cut Grades Explained

When people think about buying a diamond, they often focus on carat size or colour—but cut is actually the most important factor in how a diamond looks. A well-cut diamond will sparkle, dance with light, and appear larger and more brilliant than a poorly cut one.

In this guide, we’ll explain how diamond cut grades are determined, why they matter, and how to choose the right grade for your ring or jewellery piece.

What Is Diamond Cut?

“Cut” refers to more than just a diamond’s shape (e.g., round, oval, pear). In gemmology, cut measures how well the diamond’s facets are proportioned and aligned to reflect light.

A diamond’s cut impacts:

• Brilliance – the white sparkle from reflected light

• Fire – the coloured flashes from light dispersion

• Scintillation – the sparkle seen as the diamond moves

• Face-up size – how large the diamond looks when viewed from above

Even a flawless, colourless diamond will look dull if it’s poorly cut. That’s why cut is often called the most important of the 4Cs.

How Are Diamond Cut Grades Determined?

Cut grading is based on a combination of technical measurements, including:

• Table size (flat top surface as a % of width)

• Total depth (height of the diamond vs its diameter)

• Crown angle and pavilion angle (how light enters and reflects)

• Symmetry and polish (precision of facet alignment and finish)

Only round brilliant diamonds receive an official GIA cut grade. Fancy shapes (oval, radiant, pear, etc.) are assessed by polish, symmetry, and proportions—but don’t receive a formal cut grade.

GIA & IGI Diamond Cut Grade Scale

The GIA and IGI cut grade scale ranges from:

💡 Pro Tip: Always aim for Excellent or Very Good cut grades if sparkle is a top priority.

Cut vs Shape: What’s the Difference?

• Cut = Quality of the diamond’s craftsmanship and light performance

• Shape = The outline of the diamond (e.g., round, oval, emerald)

So while "round brilliant" is a shape, an "Excellent Cut Round" is a high-quality version of that shape.

💎 See an excellent-cut diamond in our
👉 Aeris Radiant Bezel Ring – customisable with IGI/GIA certified stones

Why Cut Affects How Big the Diamond Looks

Believe it or not, a well-cut diamond can look visually larger than a poorly cut one of the same carat weight.

Example:

• A deep-cut 1ct diamond may hide weight in the base, making the top appear smaller

• A well-proportioned 1ct diamond appears larger, with more surface area and light return

That’s why cut grade affects both beauty and perceived size.

Cut Quality in Fancy Shapes

Fancy shapes like oval, radiant, emerald, and pear do not receive an official cut grade, but polish, symmetry, and proportions still determine performance.

What to look for:

• Symmetry: Balanced curves and aligned facets

• Bowtie effect: Watch for dark areas across the centre (especially in ovals and pears)

• Depth & table percentages: Should fall within ideal ranges for the shape

At Diamond Lab, we hand-select fancy shaped lab diamonds with ideal light performance and proportions, even without a formal cut grade.

How Important Is Cut When Choosing a Diamond?

Very. While you can slightly compromise on clarity or colour, you should never compromise on cut—because it determines the diamond’s overall beauty.

Cut is especially important if:

• You want maximum sparkle

• You’re choosing a lower carat diamond and want it to look bigger

• You’re investing in a solitaire setting, where the diamond is the focal point

Lab Grown Diamonds & Cut Quality

Lab grown diamonds are cut and polished just like mined diamonds, often with more precision due to better rough yield and modern cutting tools.

Most lab diamonds at Diamond Lab are Excellent or Very Good cut and fully certified by IGI or GIA.

Final Thoughts: Why Cut Should Be Your First Consideration

If brilliance, fire, and light return matter to you (and they should!), cut is everything. Even if a diamond has a perfect clarity and colour grade, a poor cut will leave it looking flat and lifeless.

Invest in cut first, then balance colour, clarity, and carat based on your personal preferences.

Book a Consultation to Compare Cut Grades

Want to compare cut grades in person or get expert advice on choosing the best diamond for your ring? Our team can help you understand all the details—and make a choice you’ll love for a lifetime.

📍 Contact Diamond Lab today