The 4 Cs of Diamonds Explained for Engagement Ring Buyers
The four 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 useful 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 four because it determines how much light the diamond returns to your eye, which is to say how much it sparkles. Cut grades range from Excellent down to Poor. Prioritise an Excellent or Very Good cut over higher colour or clarity grades at the same price.
Colour
Diamond colour is graded from D (completely colourless) to Z (noticeably yellow or brown). For most engagement rings the best value sits in the G to I range. Those stones appear colourless or near-colourless to the naked eye but cost significantly less than D, E or F grades.
The metal affects this. In white gold or platinum, an H or I colour stone can appear slightly warm. In yellow or rose gold a slightly warmer stone is often undetectable and can complement the metal.
Clarity
Clarity refers to inclusions inside the diamond and blemishes on its surface. The scale runs from Flawless (FL) to Included (I). For most buyers VS2 or SI1 is the sweet spot: the inclusions aren't visible to the naked eye, and the stone costs considerably less than a flawless grade.
The question isn't whether the stone is perfect. It's whether the inclusions are visible without magnification. If they aren't, the clarity grade is high enough.
Carat
Carat is the weight of the diamond, where one carat is 0.2 grams. It's the most visible proxy for size but 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.
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.
At Una Diamond, centre stones of one carat and up are IGI certified and graded across all four Cs. Browse our engagement ring collection to find the right combination for your budget.
Apply the 4Cs at Una Diamond
Centre stones of one carat and up come with an IGI certificate detailing the four Cs 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 rings