What Are Diamond Cut Grades? Why Cut Is the Most Important C

Of the 4 Cs — cut, colour, clarity, and carat — cut is the one that most directly determines how beautiful your diamond looks to the naked eye. Yet it's often the C that buyers understand least. Here's a complete breakdown.

What Does "Cut" Mean?

Diamond cut doesn't refer to the shape (round, oval, emerald) — it refers to how well a diamond has been cut from the rough crystal. Specifically, it refers to the proportions, symmetry, and polish of the facets — the flat, angled surfaces that catch and reflect light.

A well-cut diamond takes in light through the table (top surface), bounces it internally between the facets, and returns it to your eye as brilliance (white light), fire (coloured flashes), and scintillation (the twinkling effect as the diamond moves). A poorly cut diamond loses that light through the bottom or sides — it looks dull, even if it has excellent colour and clarity.

How Are Cuts Graded?

For round brilliant cut diamonds, GIA and IGI both provide a cut grade: Excellent, Very Good, Good, Fair, or Poor. The Excellent grade means the proportions are optimised to maximise light return. For fancy shapes (oval, emerald, pear, etc.), there's no standardised cut grade — which is why buying from a jeweller with expertise in selecting fancy shapes matters.

Why Cut Matters More Than Colour or Clarity

A diamond with a G-colour and VS2 clarity that's Excellent cut will outperform a D-colour, IF-clarity diamond with a Poor cut — in every visual way. The cut is what makes the diamond alive.

Many buyers spend their budget chasing higher colour or clarity grades, not realising a well-cut stone with slightly lower grades will look more impressive and brilliant in person.

What to Look for When Buying

For round brilliants: aim for Excellent or Very Good cut. For fancy shapes: ask your jeweller about the specific length-to-width ratio, depth percentage, and table percentage — these determine the stone's face-up appearance. Avoid stones with overly deep or shallow depth percentages, as these indicate light loss.

At Una Diamond, we select each stone individually with care. Get in touch if you want guidance on choosing the right diamond for your budget. And explore our full range of engagement rings to see how good cut makes the difference.

See Cut Grades in Practice at Una Diamond

Every Una Diamond ring is set with an IGI-certified stone with specified cut grade. Browse our collection:

• The Georgina — oval-cut solitaire
• The Celina — emerald cut
• Solitaire rings
• Oval cut rings
• Marquise rings
• Browse all ready-to-ship rings →