The 4 Cs of Diamonds Explained: Cut, Colour, Clarity, Carat

Every diamond is graded on four characteristics — Cut, Colour, Clarity and Carat. You've probably heard the term "4 Cs" before, but here's what most guides skip: the four aren't equally important. One of them affects how a diamond actually looks far more than the others, and the rest mostly affect price and rarity. Knowing which is which will save you from overpaying for grades that make no visible difference.

1Cut — the one that matters most

Cut isn't the diamond's shape (round, oval, etc.) — it's how precisely its facets are angled to reflect light. A diamond cut to ideal proportions bounces light back up through the top, creating the brilliance and sparkle a diamond is prized for. A poorly cut diamond can leak light out the sides or bottom, looking dull even with excellent colour and clarity. If you only prioritise one C, make it this one — it has the biggest visible impact of all four, and it's the one imperfect cutting can't fix later.

2Colour — graded on what's not there

Diamond colour is graded on an absence of colour, from D (completely colourless) down through the alphabet as a faint yellow or brown tint increases. Here's the practical part: differences between adjacent grades are extremely subtle, and once a diamond is mounted in a ring — especially in yellow or rose gold, which flatters warmer tones — grades several steps apart can be genuinely difficult to tell apart with the naked eye. G–I colour is a common sweet spot: still reads white, without paying peak price for D–F.

3Clarity — mostly invisible past a certain point

Clarity measures internal inclusions and surface blemishes, graded from Flawless down to Included. Most inclusions at the SI1–SI2 grade are completely invisible without 10x magnification — meaning you can often buy two clarity grades lower than "flawless" and see zero visible difference, while paying substantially less. The exception: step-cut shapes like emerald and asscher have larger, more open facets that show inclusions more readily, so it's worth grading slightly higher for those specific shapes.

4Carat — weight, not size

Carat is simply weight (0.2 grams per carat) — not a direct measure of how large a diamond looks. Shape, cut depth and table size all affect how big a given carat weight actually appears once set. We cover this in more depth in our carat weight guide — worth a read if size is a priority for you.

Putting it together

The 4 Cs work together, not independently — a smaller diamond with an excellent cut will often outshine a larger one cut poorly. The right balance between all four always comes down to your own priorities and budget, which is exactly why comparing a few real stones side by side is so much more useful than chasing a "perfect" grade on paper.