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The 4Cs of diamonds

The 4Cs of Diamonds

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How to choose a diamond

Choosing a diamond isn't simple; to get it right, you'll need to understand the 4Cs of diamonds, which we explore in detail below. You'll need to do your research and take your time comparing different diamonds to ensure you find the best diamond for you.

We aim to make finding the perfect diamond an exciting and rewarding experience, and if we can be of any assistance, please feel free to get in touch.

What are the 4Cs?

The 4Cs are the four main factors that determine the beauty and value of a diamond:

It's essential to consider each of the 4Cs carefully. Choose unwisely, and you may end up with a dull-looking diamond with a yellow hue and unsightly blemishes.

To know what you're looking for and avoid surprises, it's essential to understand each of the 4Cs and how they are graded. 

The Gemological Institute of America (GIA) developed the concept of the 4Cs in the 1940s and helped to standardise diamond grades and terminology worldwide.

Loose diamonds of various shapes

Carat Weight

The weight of diamonds (and other gemstones) is measured in carats, with one carat equal to 0.2g. As the weight of a diamond increases with volume, carat weight is synonymous with diamond size.

Carats are divided into one hundred points (0.002g each), so a 1.5ct diamond, for example, is 150 points.

Whilst we commonly see diamonds weighing nice round numbers like 0.5ct, 1ct, and 1.5ct, diamonds actually come in all sizes and weights.

For many people, it is a priority to try to buy the largest diamond they can with their budget, but you should also consider the quality of the diamond, which is where the other three Cs come in! Most people would prefer a slightly smaller stone that is bright white, flawless to the naked eye, and sparkles beautifully to a larger stone that is tinted, dull and has visible imperfections.

Confusingly, the same word ('carat' or 'karat') has a second completely different meaning within the jewellery industry, being used to describe the purity of gold. 24ct gold, for example, is pure gold, whereas 18ct gold is 75% pure. 

Colour Grades

The colour of a white diamond ranges from colourless through to a light colour, most often a light yellow or light brown. Diamonds with greater colour saturation than "light" are known as fancy coloured diamonds.

The white diamond colour-grading scale is alphabetical and runs from D (completely colourless) through to Z (light colour). Diamonds graded D, E or F are all considered colourless, while G, H, I and J are near colourless. Generally speaking, most people begin to be able to discern some colour in diamonds below G colour but struggle to distinguish between the higher grades, which all look white to the untrained eye.

GIA diamond colour scale chart
GIA Diamond Colour Scale Chart

While gem-quality white diamonds are rare, fancy coloured diamonds are even rarer, making them incredibly valuable. Fancy coloured diamonds, including yellows, pinks, blues, greens and reds, are graded for colour on a different scale that runs from Light Fancy to Deep Fancy.

Clarity Grades

Diamond clarity refers to the presence of imperfections either inside the diamond (inclusions) or on its surface (blemishes). These are present in all diamonds, but when diamonds are being graded for clarity, this is performed under 10x magnification, and diamonds with no imperfections visible at 10x magnification are graded as Flawless (FL).

GIA diamond clarity scale chart
GIA diamond clarity scale chart

The main factors impacting how visible any imperfections are, and therefore diamond clarity, include:

  • Size - smaller imperfections generally being less visible than larger ones.
  • Number - fewer imperfections being preferable to more imperfections.
  • Colour - darker inclusions and blemishes generally being more visible than paler imperfections.
  • Location - inclusions located nearer to the top surface of a diamond or more centrally positioned (when viewed from above) are generally more prominent than those found deeper with the diamond or nearer to the "edges" (when viewed from above).

The GIA diamond clarity scale goes from FL (flawless) down to I2 (heavily included). As you move down the clarity scale, the imperfections become increasingly prominent. Still, generally, you would need to go down to the Slightly Included grades (SI1 or even SI2) before the imperfections were visible to the naked eye and down to the Included grades (I1 and I2) before the inclusions began to impact the sparkle of a diamond. Diamonds with no imperfection visible to the naked eye, typically VS2 clarity or higher, are described as "eye clean".

There are many different types of inclusions found in diamonds, some of the most common being:

  • Crystals
  • Pinpoints
  • Clouds
  • Graining
  • Twinning wisps 
  • Feathers
  • Cavity

Cut Grades

Confusingly, the term cut is used to mean three different things in the context of diamonds.

  • The cut grade (round brilliant cut diamonds only) - the last of the 4Cs
  • The shape (round cut vs cushion cut, for example) - not one of the 4Cs
  • The type of diamond faceting (brilliant cut vs stepped cut, for example) - also not one of the 4Cs

The cut grade is an assessment of the relative proportions of a round brilliant cut diamond, with two of the primary considerations being the depth percentage (depth as a percentage of width) and table percentage (width of the top facet, known as the table, as a percentage of the width of the diamond as a whole).

The cut is responsible for how much light enters the diamond and how much is reflected and refracted (the light performance) - which determines how brightly it sparkles.

A well-cut diamond will produce maximum sparkle, whereas a poorly cut diamond will see the light leak out of the bottom of the stone, resulting in a duller appearance.

The GIA cut grades run from Excellent down to Poor. We recommend our clients only consider Excellent or Very Good cut. The price premium is usually relatively modest, and its impact on the appearance of a diamond is usually well worth it.

diamond cut guide
GIA Cut Grades

Some other gemological authorities use slightly different grades, with the International Gemological Institute having a category called Ideal Cut which sits above their Excellent Cut grade.

There is no consensus on the optimal proportions for fancy cuts, so reputable gemological laboratories do not ascribe them a cut grade as such. They are, however, given 'polish' and 'symmetry' grades (as are round brilliant cuts).

Diamond shapes

Often, when people refer to a diamond's cut, they are actually talking about its shape, which is not one of the 4Cs.

Diamond Shapes Chart
Popular Diamond Shapes

Diamonds can be cut into a wide variety of shapes. By far, the most popular is the round brilliant cut. All other shapes are collectively known as fancy cuts, the most popular being:

Types of faceting

The term 'cut' is also used to describe different styles of diamond faceting: 'step cut' vs 'brilliant cut' vs 'rose cut' for example. Again, this is not one of the 4Cs!

Square or rectangular stones whose facets are cut in parallel straight lines are known as step cuts, the most famous being the emerald cut. Step cuts prioritise weight preservation and the reflection of light over refraction. As a result, they are more inclined to exhibit flashes of white light than to sparkle.

Brilliant and modified brilliant cuts, on the other hand, have triangular and kite-shaped facets which increase the refraction of light, creating more of a sparkle, but at the expense of weight loss and a reduction in the amount of reflected light.

Mixed cuts share aspects of both brilliant and step cuts, combining some of the weight preservation and dimensions of step cuts with the sparkle of brilliants. The most popular example of this is the princess cut.

Rose cuts are very different from both step cuts and brilliants, having a flat base, and are very rarely seen these days, except in antique jewellery.

Which is the most important of the 4Cs?

Each of the 4Cs plays an important role in a diamond's overall appearance, so we advise our customers to take a balanced approach. There is little point in prioritising one of the 4Cs at the expense of the others. A colourless diamond with large imperfections or a flawless diamond that is noticeably discoloured is probably a worse choice for most people than a near colourless with very small inclusions that are only visible under magnification.

The Fifth C: conflict-free

IR 001 edited

At Ingle & Rhode, we only source ethical diamonds that we can trace back to the mine of origin. This way, we can guarantee that all of our diamonds are conflict-free.


A diamond engagement ring is a very significant purchase, both financially and emotionally, and so we highly recommend taking your time to understand the 4Cs and using this understanding to find the perfect diamond for you and your partner.

Generally speaking, if you want a diamond that looks a good white colour, we recommend a minimum of G colour. If you want a diamond with no imperfection visible to the naked eye, we recommend a minimum of VS2 clarity. And if you want a diamond with maximum sparkle, we recommend an Excellent cut (or for an IGI-certified diamond, an Ideal cut or Excellent cut).

Almost all of our diamonds of 0.3ct and above are supplied with laboratory certificates, which summarise how an independent gemologist has graded the diamond against the 4Cs.

If you have any questions on the 4Cs or require some guidance, we'd be delighted to help and would be happy to show you a selection of loose diamonds of different shapes, sizes and grades.

Tim Ingle
Together with David Rhode, Tim created Ingle & Rhode to offer a better alternative to the traditional luxury brands. Since 2007, we’ve provided our customers with genuinely ethical engagement rings, wedding rings and fine jewellery – free from conflict diamonds, dirty gold and child labour. With more than 16 years experience in the jewellery industry, Tim has deep expertise in diamonds, gemstones and jewellery design and manufacturing.