The 4Cs are cut, colour, clarity and carat, the four qualities used to grade every diamond and, taken together, to set its price. This guide explains what each one means, which of them matters most to how a diamond actually looks, and how to what to consider when choosing one.
The 4Cs of a diamond are cut, colour, clarity and carat. They were set out by the Gemological Institute of America, the GIA, and are the standard way every diamond is graded. Of the four, cut has the greatest effect on how a diamond looks, so it is the one worth prioritising.
What are the 4Cs of a diamond?
The 4Cs are the four measures used to grade a diamond's quality: cut, colour, clarity and carat. They were defined in the mid twentieth century by the Gemological Institute of America, an independent body usually shortened to the GIA, and they gave the trade a shared language for describing a stone. Before them, terms like "fine" or "river white" meant different things to different sellers.
Each C describes something separate. Cut is how well the diamond has been shaped to handle light. Colour is how little colour it holds. Clarity is how few natural marks it has. Carat is its weight. A grading report scores all four, and together they decide both how the diamond looks and what it costs. The useful thing to understand early is that the four do not matter equally, which is where we will start.
Cut: how a diamond handles light
Cut is the most important of the 4Cs, because it decides how much a diamond sparkles. It refers to how well the stone has been shaped and polished, its proportions, symmetry and finish, and therefore how its facets catch light and send it back to your eye. Cut is not the same as shape. Shape is the outline, round or oval or pear, while cut is the quality of the work within that shape.
When a diamond is cut well, light enters through the top, bounces around inside and returns as brightness and flashes of colour. When it is cut too deep or too shallow, light leaks out of the bottom or the side, and the stone looks dull or dark no matter how good its other grades are. This is why cut is worth prioritising: a beautifully cut diamond with an average colour and clarity grade will nearly always look better than a poorly cut one with top grades everywhere else.
The GIA grades cut from Excellent down through Very Good, Good and Fair to Poor. Some labs, including the IGI, add an Ideal grade at the very top. For a stone you want to sparkle, aim for the upper end of whichever scale is on its report. If you are choosing between diamond shapes, our guide to diamond shapes explained covers how shape and cut work together.
Colour: how white the diamond is
Colour grades how little colour a diamond holds, running from completely colourless down to a faint yellow or brown tint. Counterintuitively, less colour is rarer and more valued, so the best grades are the ones with no colour at all.
The GIA colour scale runs by letter from D to Z. D, E and F are colourless. G through J are near colourless, meaning any tint is so slight it is very hard to see once the diamond is set, especially from the top. From K onward a warm tint becomes easier to notice. For most people the sweet spot is the near colourless range, because a G or an H looks white to the eye but costs noticeably less than a D. The metal matters too: a faint tint hides more easily in yellow or rose gold than against white gold or platinum.
Clarity: the diamond's natural marks
Clarity measures the tiny natural marks a diamond carries, inside and on the surface. The internal ones are called inclusions and the surface ones blemishes, and nearly every diamond has some, formed as the crystal grew under heat and pressure deep in the earth. Fewer and smaller marks mean a higher clarity grade.
The GIA clarity scale has eleven grades. Flawless (FL) and Internally Flawless (IF) sit at the top, followed by two grades of Very Very Slightly Included (VVS1 and VVS2), two of Very Slightly Included (VS1 and VS2), two of Slightly Included (SI1 and SI2), and finally Included (I1, I2 and I3), where the marks are visible to the naked eye.
The idea that matters most here is "eye clean", which means a diamond whose inclusions you cannot see without magnification. A carefully chosen VS2 or SI1 diamond is usually eye clean, and to anyone looking at it, it appears just as flawless as a stone graded far higher. Paying for VVS or Flawless mostly buys perfection that only a jeweller's loupe can see. One caution: not every stone in the VS2 to SI1 range is eye clean, so it is worth having each one checked rather than trusting the grade alone.
| The C | What it grades, and the scale |
|---|---|
| Cut | How well the diamond returns light. Excellent to Poor, with Ideal at the top on some reports. Matters most to how it looks. |
| Colour | How little colour it holds. D (colourless) to Z (tinted). Near colourless, G to J, is the value range. |
| Clarity | How few natural marks it has. Flawless to Included. Eye clean, often VS2 or SI1, is the value range. |
| Carat | Its weight, not its size. One carat is 0.2 grams. |
Carat: weight, not size
Carat is the weight of a diamond, not its size. One carat is 0.2 grams, and it is divided into 100 points, so a quarter carat diamond is 25 points, or 0.25ct. Because carat measures weight, two diamonds of the same carat can look like different sizes depending on how they are cut and what shape they are.
As a rough guide, a well cut 1ct round diamond measures about 6.5mm across the top. A deep cut stone can hide some of its weight below the surface, so it weighs the same but looks smaller from above, which is another reason cut is worth getting right. Elongated shapes like oval and marquise tend to look larger than a round of the same weight because they carry more of their size across the top. Our guide to diamond carat weight and size has a size by shape chart if you want to picture it.
Which of the 4Cs matters most, and how to prioritise
Cut matters most, and after that the order depends on your eye and your budget rather than on any fixed rule. The mistake worth avoiding is spending on the grades you cannot see, at the cost of the one you can.
Prioritise cut first, since it does the most for how a diamond looks. Then choose a near colourless grade and an eye clean stone rather than the top of each scale, and let carat be whatever your budget allows once the other three are right. That order gives you the best looking diamond for the money.
That is the short version of how to balance the four. For the full method, including how this plays out across the pieces we make, see how to choose a diamond. It is also worth knowing that lab grown diamonds are graded on exactly the same 4Cs, a point we cover in lab grown vs natural diamonds. Everything here sits under our wider guide to diamonds.
Once you understand the 4Cs, the easiest place to see them at work is a simple piece where the diamond is the whole point, like a pair of diamond stud earrings or a diamond tennis bracelet.
