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Quick Guide to GIA Diamond Grading

Last updated on March 04, 2024

Before the 1940s and 50s, jewellers and jewellery consumers lacked a reliable and standardised way to describe diamonds. Of course, carat weight was always a determining cost factor, but buyers often had to trust a jeweller's discretion regarding other traits.

Then in the mid-twentieth century, the Gemological Institute of America (GIA) created a common language for diamonds, providing a consistent way to describe a stone's unique characteristics.

The GIA International Diamond Grading System™ institutionalised what we now call ‘the 4Cs,’ and buyers and sellers began to use this consistent, accurate way to communicate diamonds' values. 

Let's explore the GIA grading system.


The 4Cs of Diamonds

When making an expensive purchase, people want objective data on which to gauge their risk. The GIA Diamond Grading Report provides scientifically determined facts about diamond shape, colour, clarity, cut, carat weight, proportions, and finish. So let's take a closer look at the 4Cs: colour, clarity, cut and carat.


When we talk about diamond colour, we're referring to the absence of colour. A chemically pure, structurally perfect diamond is like a drop of water: it has no hue. Therefore, GIA's colour grading system awards higher ratings to colourless stones.

GIA's D-to-Z colour-grading system establishes a stone's degree of colourlessness, so customers can easily compare diamonds. Most of these distinctions are subtle and invisible to the untrained eye. But GIA experts compare stones under controlled lighting and precise viewing conditions. If you're looking for a chemically pure diamond, you'll seek a stone with a D, E or F rating.


Natural diamonds result from carbon exposed to intense heat and pressure deep below the earth's surface. But, unfortunately, the process that produces diamonds also tends to result in internal flaws called 'inclusions' and external traits called 'blemishes.'

When the GIA uses the term 'clarity,' it refers to the absence of inclusions and blemishes. To describe a stone's clarity as accurately as possible, the GIA has created a scale with six categories, some of which are subdivided.

  • Flawless (FL): No inclusions or blemishes visible under 10x magnification

  • Internally Flawless (IF): No inclusions visible under 10x magnification

  • Very, Very Slightly Included (VVS1 and VVS2): Inclusions so slight that they're difficult for a skilled grader to see under 10x magnification.

  • Very Slightly Included (VS1 and VS2): Inclusions are observed with effort under 10x magnification, but they can be characterised as minor.

  • Slightly Included (SI1 and SI2): Inclusions are noticeable at 10x magnification.

  • Included (I1, I2, and I3): Inclusions are noticeable under 10x magnification. These flaws may affect transparency and brilliance.


Diamonds are famous for the way they sparkle, and they owe this trait to expert diamond cutters. People tend to think of a stone's cut as shape (brilliant, oval, marquise, and so on), but 'cut' actually refers to how well a diamond's facets interact with light. A high-value diamond has precise artistry and workmanship. A magnificent sparkle is the result of impeccable proportions, symmetry and polish.

GIA calculates the proportions of a diamond's facets that influence its face-up appearance to grade a diamond's cut. The GIA Diamond Cut Scale for brilliant round diamonds (the most popular shape) contains five grades ranging from Excellent to Poor. The system studies how successfully a stone interacts with lights to create the following visual effects:

  • Brightness: White light reflected from a gemstone

  • Fire: The degree to which white light scatters into all the colours of the rainbow

  • Scintillation: The pattern of light and dark areas caused by reflections within the diamond

Carat Weight

Carat weight is the most straightforward measurement defined by the GIA. Simply put, carat measures how much a diamond weighs. A metric 'carat' equals 200 milligrams, and each carat is divided into 100 'points'. Therefore, a jeweller may refer to a 0.25-carat diamond as a 'twenty-five pointer .' Likewise, a 1.09-carat sparkler could be described as 'one point oh nine carats.'

All other characteristics equal, diamond prices increase with carat weight because larger stones are rarer. But it's essential to keep in mind that two diamonds of equal carat weight can have vastly different prices depending on the three other 4C factors mentioned above (colour, clarity and cut). 


Benefits of GIA Diamond Grading

When shopping for a diamond, always ask for the lab reports of stones you want to compare. In addition, understanding the benefits of GIA Diamond Grading can help you make a wise decision.


Anywhere you buy or sell diamonds, people will understand the gemstone's grading report and have faith in the sparkler's authenticity. Even if you're purchasing a diamond overseas or from a new jeweller, you can trust the stone's authenticity if it's accompanied by GIA certification.

Quality Data

GIA is a third-party organisation that doesn't affiliate with particular jewellers. Therefore, you can trust the data as you weigh your options. Furthermore, GIA has an impeccable reputation; you don't have to worry about the information's source.


A GIA Diamond Grading Report is helpful not just when you're purchasing a diamond but it will also benefit you when you sell. Just as you look to a third-party source of information when purchasing a ring or luxury watch, people will also do the same when they buy a piece you're re-selling. Therefore, you should keep your grading report in a safe place where you'll be able to find it later.

Once you find the perfect diamond, you'll need to protect it! Get a free, instant quote to learn how affordable it can be to insure your engagement ring.

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