The 4 Cs of Diamonds Explained for Engagement Ring Buyers
The 4 Cs — cut, colour, clarity, and carat — are the universal language of diamond quality. Every certified diamond in the world is assessed against these four criteria, and understanding them is the single most important thing you can do before buying an engagement ring.
Cut
Cut refers to how well a diamond has been shaped and faceted from the rough crystal. It's the most important of the 4 Cs because it determines how much light the diamond returns to your eye — in other words, how much it sparkles. Cut grades range from Excellent (the best) to Poor. Always prioritise an Excellent or Very Good cut over higher colour or clarity grades at the same price point.
Colour
Diamond colour is graded on a scale from D (completely colourless) to Z (noticeably yellow or brown). For most engagement rings, the "sweet spot" for value is in the G to I range — these stones appear colourless or near-colourless to the naked eye, but cost significantly less than D, E, or F grades.
The metal you choose affects this: in white gold or platinum settings, an H–I colour stone can appear slightly warm. In yellow or rose gold, a slightly warmer stone is often undetectable and can even complement the metal beautifully.
Clarity
Clarity refers to the presence of inclusions (internal characteristics) or blemishes (surface characteristics) in the diamond. The scale runs from Flawless (FL) to Included (I). For most buyers, VS2 or SI1 clarity is the sweet spot — the inclusions aren't visible to the naked eye, but the stone costs considerably less than a flawless or internally flawless grade.
The key question isn't "is this stone perfect?" but "are the inclusions visible without magnification?" If the answer is no, the clarity grade is high enough.
Carat
Carat refers to the weight of the diamond (1 carat = 0.2 grams). It's the most visible proxy for size, but it's not the only factor — cut quality and shape significantly affect how large a stone appears face-up. A well-cut oval can look considerably larger than a round of the same carat weight, for example.
Popular sizes for Australian engagement rings in 2026 are 1.0ct to 1.5ct. With lab-grown diamonds, you can often afford a larger stone for the same budget — making the 4 Cs stretch further than they would with a natural stone.
All Una Diamond rings are set with IGI-certified stones graded across all 4 Cs. Browse our engagement ring collection to find the right combination for your budget.
Apply the 4Cs at Una Diamond
Every Una Diamond ring comes with an IGI certificate detailing the 4Cs of your stone. Browse our handcrafted engagement rings:
- The Georgina — oval-cut solitaire
- The Celina — emerald cut
- Solitaire rings
- Oval cut rings
- Emerald cut rings
- Browse all ready-to-ship rings →