The 4 C’s, Diamond Grading Guide.


Alongside being a girl’s best friend, Diamonds have become one of the highest symbols of affluence and affection in our world.

The name is derived from ancient Greek adámas meaning “unbreakable” and “unalterable” since diamond is the strongest mineral on Earth, formed of highly concentrated carbon subjected to immense pressure and high temperatures.  

Rough diamonds are mined, cut and polished to reveal the brilliance of the stone,  they are then valued by professional diamond graders.  

The value of a diamond is graded according to 4 factors, called the 4C’s.  

  • Cut: In simple terms, the cut refers to the shape as well as the reflective quality of the diamond.
  • Clarity: Some diamonds contain blemishes, which occur during formation and affect how clear the diamond appears.
  • Colour: Colourless diamonds sparkle more brilliantly due the colour absorbing light.  
  • Carat Weight: Diamonds’ size, dimension, and weight are measured in metric carats.  

4 C’s in Detail:


The diamond cut is one of the most important variables which are referred to in 2 different ways, its shape and its reflective qualities,  the second being what is graded and what affects the value of the diamond.  

The brilliance and sparkle of the diamond is determined by the cut.  With an excellent cut the light is better reflected and the diamond therefore has more radiance.    

In an ideal cut diamond, the light enters the stone and is perfectly reflected through the pavilion from one side to the other and then back out through the diamond.  This reflection causes the twinkle effect that is seen and admired, and the reason a diamond looks almost alive.  

In a poor cut diamond, the light enter the pavilion and is reflected not through the top but rather the sides or bottom of the stone.  This causes the light’s reflection to be lost and the diamond to lose its brilliance.

The ideal cut is achieved using a set of formula which gives a perfect proportion between the size and the depth of the diamond to enhance the light reflection.  

The grades of diamond cuts are categorized as the following:

  • Ideal cut: Maximum light reflection
  • Excellent cut: Slightly less reflection than the ideal
  • Very good cut: Reflects most of the light that enters the stone
  • Good: Some light is reflected and some is lost
  • Fair and poor: Not much light is reflected.  


This grade is determined by the amount of flaws that a diamond contains, technically termed “inclusions” and “blemishes”.  Blemishes are found on the surface of the stone and inclusions are found within, which is an expected occurrence since diamonds are naturally formed. The first and highest grading of a diamond is Flawless (F) which means it contains absolutely no inclusions,  the last grading is Inclusion 3 (I3) meaning blemishes and inclusions are visible.  

Clarity gradings are categorized as the following:

  • F (Flawless):  Diamonds that have no inclusions or blemishes, with near perfect clarity, which are very rare.
  • IF (Internally Flawless):  No inclusions within the diamond, with slight blemishes to the surface. Also very rare.
  • VVS1/VVS2 (Very Very slight inclusions): As the name suggests, there are 1 or 2 tiny inclusions, but still considered near perfect diamond.
  • VS1/VS2 (Very slight inclusions): Also very slight inclusions that not visible to the naked eye. Used in high end jewellery.
  • SI1/SI2 (slight Inclusion): Tiny inclusions that may be visible to the naked eye.  Still a good choice the most popular sold diamond clarity category.
  • I1/I2/I3 (Inclusion): Flaws visible to the naked eye, not a popular choice.  


The colour of a diamond is graded in relation to the absence of colour in a white diamonds,  and  the more “white” the diamond’s colour is, the more valuable the diamond.  This is because colour absorbs light, and therefore the more colour a diamond has, the more light would be absorbed and not refracted.  

Colours of diamonds are graded from the highest being the letter D (No Colour) through to the letter Z , the latter having a dark colour appears with little to no light being refracted.  

Colour gradings are categorized as the following:

D-F: Quite rare diamonds having a brilliant sparkle.  They are the most prized colour choice, being pure white or no colour.

G-I: Still considered a very good colour, being very near pure white.  Also the most popular choice of colour.  

J-M: Appearance of a slight yellow tint.  These diamonds are sometimes set in necklaces and earrings, or clusters where the colour is not noticeable.  Not a popular choice for engagement rings.

N-Z: Darker yellow colour tint with very little refraction of light.

And while coloured diamonds are very valuable, where the more intense the colour the more precious the diamond, this has no relation to the colour grading of white diamonds.

Carat Weight

The carat is the weight measurement of the diamond.  Diamonds that are less than a carat are called pointers by the jewellery trade. Large diamonds are very rare in nature and therefore value rises exponentially with the carat weight.  

The abbreviation for carat weight is ct, and the abbreviation TW refers to the total carat weight of the piece of jewellery.   If a piece of jewellery contains 10 diamonds of an equal size, and the total carat weight is 0.5ct, then each diamond weighs 0.05ct or 5 pointers.  

Approximate guide to round diamonds:

a 0.5ct diamond is 5.1mm, 0.75ct diamond is 5.8mm, a 1ct is 6.5mm and 2ct carat is 8.1mm.

Approximate guide to prince cut or square diamonds:

a 0.5ct diamond is 4.4mm, 0.75ct is 5mm, a 1ct is 5.5mm and a 2ct is 7.0mm.