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In this diamond guide, you'll learn how a diamond's cut influences how they interact with light. In addition, their shapes, how they are made up and more!
5 Mins

Diamond Four Cs Guide: Cut

Lewis Findley
Lewis Findley

Diamond Cut and Shape Guide

Did you know that no two diamonds are the same?

The cut of a diamond can be the difference between one which is dull and another which you'll never forget.

It's made cut the most important of the Four Cs because it affects the way the diamond interacts with light to create that sparkle and brilliance.

But, how do you choose the right cut? what's the difference between cut and shape? How are they graded?

In this guide, you'll learn about all of that and more!

So, what happens when a diamond is found and what's the journey it takes before it's in the shop window?

How Are Diamonds Cut?

So, a diamond is found in its rough form but once it's cleaned, it will then be analysed to see what the best cut is.

The goal? To identify the cut that will produce either the highest quality diamond(s) or the biggest diamond from that rough stone.

Once the decision is made, the rough diamond is marked to indicate the areas which need cutting.

What is diamond cut?

The cut of a diamond refers to the quality of its proportions, symmetry and polish.

  • Proportion - The ratios and/or sizes of the diamonds width, table and depth.
  • Polish - To maximise brilliance, the surface of each facet needs to be polished.
  • Symmetry - The degree of quality in the diamond's facets. If symmetry is achieved, they'll be able to hold more light and produce a high sparkle.

The higher quality the cut, the more light can be emitted from the diamond. There's a diamond cut chart which helps to illustrates this.  

Diamond Cut Chart

In this diamond cutting chart, you'll learn how different cutting techniques can influence how light interacts with a diamond.

Diamond Cutting Chart

Image Via - Livia Diamonds

From the diamond cut chart, you can see how an ideal cut diamond can emit the most light. 

It creates that brilliance, scintillation and fire which brings a diamond to life for the viewer but, what are they?

  • Brilliance – The total amount of light reflected and refracted in the diamond. The more brilliance, the brighter the light.
  • Scintillation - Whilst light travels through the diamond's facets and angles, it gives off a sparkle or flashes of light which is the scintillation.
  • Fire - The transformation of light into different colours such as blue, green and purple. This is called fire and you can see this on the diamond's crown.

Now that you know the different ways a diamond can be cut to maximise their potential, what shapes can they be?

What is diamond shape?

The diamond's shape refers to the outline of the diamond.

That is to say, a diamond's shape could be round, princess, emerald, Heart, Marquise and more. Check out this diamond shape chart which shows different diamond shapes. 

Diamond shape chart

Image via - Bicknells

Hatton Garden are a world renowned jewellery centre in the UK and they revealed that the round brilliant diamond is the most popular diamond shape.

To determine the quality of the cut, they can be graded with charts from leading authorities such as GIA and AGS to determine their quality.

How are diamonds graded?

The Gemological Institute of America (GIA) is a worldwide authority on diamonds and created a chart to certify the cut quality of diamonds.

Starting from Excellent, it's a sliding scale which ends at poor. 

It must be noted that the American Gem Society use ideal as their highest grade. 

  • Ideal – Reflects the majority of light which enters the diamond (highest grade for AGS).

    Note - This category applies only to round diamonds.
  • Excellent - Reflects as much light as an ideal certified diamond (highest grade for GIA).
  • Very Good – Most of the light entering the diamond is reflected through the top of the diamond which tends to be bigger. 
  • Good - Reflects a high amount of light but appears darker in comparison to diamonds graded higher. Diamonds of this grade are usually cut from the original rough stone.
  • Fair & Poor – Can appear dull or glassy. These diamonds have been cut to maximise carat weight. In addition, diamonds of these grades leak light at the bottom of the diamond.

Parts of a diamond

parts of a diamond

When you break down a diamond, it contains different aspects:

  • Table - This is the flat top of a diamond.
  • Girdle - The rim of a diamond that separates the crown and the pavilion. 
  • Culet - The tip of the bottom part of a diamond (pavilion).
  • Depth - From top to bottom, the height of a diamond. (also called height).
  • Pavilion - Sometimes called the base of a diamond, it's the lower part of a diamond (below the girdle).
  • Crown - The upper part of a cut gemstone (located above the girdle).
  • Width - A diamond’s width is measured from one of the girdle to the other. 

Diamond width, depth and table 

Now that you know the parts of a diamond, you can increase your understanding with percentages and ratios used to describe various aspects of them.

These percentages concern the table, depth and width of the diamond.


To determine the table %, divide the width of the table's surface area with by the width of the diamond (also called the diameter).

For example, a 3.5mm table and 6mm width equals a table of 58.3%.

If the percentage is too big, light won’t reflect off the diamond’s facets. If the percentage is too low, light stays trapped inside the diamond and escape elsewhere.  


The depth percentage is measured by dividing the depth (or height) by the width of the diamond. This percentage can give an early indication of how well the diamond interacts with light.

For example, if a diamond has a depth of 6mm and a width of 8mm, the depth percentage is 75%.

To create the best relationship between depth and light, it depends on the diamond shape and how well the facets are proportioned. 

Length to Width Ratio

This ratio helps to explain how proportionate the diamond is. 

The higher the ratio, the more elongated and the lower the ratio, the more square or short it is.

Don't worry! There's a standard range for each diamond shape.

Final Words

Diamonds are truly worth a thousand words.

A fascinating marvel. The fire, sparkle, brilliance or shape - the way light transforms a diamond is incredible and further strengthens our bond with these beautiful stones.

The precision and quality of a diamond’s cut, namely its proportions and symmetry, greatly impact a diamond’s beauty and price.

Now that you have a greater understanding of cut, you can explore further into The Four Cs and become your own diamond expert!

If you want to explore our collection of diamonds and luxury jewellery then check out our catalogues!

Next in the series is clarity which you can read by clicking the button below!