What is the Best Diamond Grade? Understanding the 4Cs of Diamonds

| 7 min read

I’m going to start this right off by changing the title to ‘What is the Best Diamond Grading for Me, at My Budget?’. That’s the thing about Diamonds, there are so many to choose from, and it can be really difficult to cut through the marketing hype and work out what the best Diamond is for you. So what do you need to think about when buying a Diamond?

First of all, it’s important to remember that a natural Diamond is exactly that, natural. A Diamond created in a lab will be ‘perfect’, but when you become a custodian of a real Diamond, one of Mother Nature’s treasures, you will have a unique work of art, with a completely distinctive character.

You may know that when you’re choosing a Colourless Diamond, you need to be looking at the Four Cs:

  • Cut
  • Carat Weight
  • Colour
  • Clarity

The Diamond industry has generally adopted the GIA (Gemological Institute of America)’s Diamond grading scale. In this blog, I’m going to talk you through how the scale works, and explain why the very top grades aren’t necessarily the best choice for most collectors.


The quality of the cut is the responsibility of a lapidarist or gemstone cutter. Diamonds can be any of a variety of shapes (heart, marquise, antique cushion for example) but many are cut into what's known as a 'round brilliant'. This was perfected by Marcel Tolkowsky in 1919 and continues to be used to this day with very few alterations.

Tolkowsky described the perfect dimensions and facet positions to maximise the fire and brilliance of a Diamond, as he realised that a cut that was too shallow or too deep would reduce in the loss of light out of the bottom and sides of the stone. The amount of scintillation (sparkle) must be taken into account too. The word 'cut' can often be confused with shape. Think of 'cut' in this context as the quality of the cutting, not the specific shape of the Diamond you are buying. In terms of buying a Diamond, what you're looking for is good all-round symmetry, and a good amount of fire, brilliance and scintillation.

Ultimately, beauty is in the eye of the beholder, so as long as you're happy with what you're seeing then a lot of the technical information that determines a cut is probably moot. If you want to be sure, however, ask your jeweller if the cut has been graded. The GIA grades Diamonds as Excellent, Very Good, Good, Fair and Poor.

Carat Weight

How big do you want your Diamond to be? This may seem like a straightforward choice of picking the size you can afford, but not every Diamond of the same carat weight will cost the same as you must take into account the other three Cs. An internally flawless D colour 2ct Diamond with an excellent cut will cost a lot more than an I3 Z coloured 2ct Diamond with a poor cut. Buying the perfect Diamond for you is all about balancing your budget with the size you want and how important the colour and clarity grades are to you, which we'll get on to now.


When it comes to the colour of a Diamond, the grading is on an alphabetical scale from D to Z. (This may seem odd, but it’s because it was developed by the GIA to replace the old A-C grading system!) D is the most colourless, all the way through to Z, which is termed ‘light yellow’. Anything more yellow than Z is a fancy coloured Diamond.

Incidentally, Diamonds are the only gemstones where the colour is judged face-down. This is because a Diamond is singly refractive, so the colour will be the same either way up, and at the same time, if you were to judge a Diamond from the front, the brilliance and fire from a well cut stone would be a distraction to the grader.

The Diamond colour scale is split into groups – as you can see below:

GIA colour chart

Here at Gemporia, we usually recommend G-H graded Diamonds. I’m sure a lot of you will be quick to point out that G-H isn’t the best colour grading on the market. This is true, and while some jewellers will stock D-F graded Diamonds, we don’t recommend them because we don’t think that they’re the best value.

Let me explain – if you’re looking at trade prices in February 2016 for, let’s say, a round cut, 4 carat IF (I’ll explain what this means in a moment) Diamond, a D colour grade would cost you $87,750 per carat. On the other end of the scale, an M colour grade would be $10,100 per carat. This is a huge difference in price! We would say that M is too yellow, but G-H is a perfect compromise, and comes in at $35,600 – $47,000 per carat, a huge saving on the ‘best’ grade.

Now here’s the thing – unless you are comparing them side by side (and who does that?) I’d defy anyone to tell the difference between a D grade and a G-H. In the industry, G-H grades are known as ‘Ice White’, and the vast majority of Diamonds you will see in shops are of this grade.


When it comes to the clarity grading of a Diamond, the GIA uses the following scale:

GIA clarity chart

The most important thing to remember with this scale is that FL all the way through to I1 are eye-clean. This means that they look perfect to the eye. All other gemstones are only graded by eye, but Diamonds are graded under 10X magnification.

Diamonds are a relatively common gemstone as gemstones go, and this grading system was essentially introduced to increase the ‘appearance of rarity’. Don’t just take my word for it. Richard Wise, one of the world’s foremost gem connoisseurs, in his book Secrets of the Gem Trade, calls the clarity grading of a Diamond ‘an absurdly stringent standard of judgement’. He goes on to explain that between a FL and I1 graded Diamond ‘from the perspective of beauty […] there is no difference at all’.

The grading system above I1 is essentially arbitrary, since by definition, there is no difference when viewed with the naked eye. This is why, here at Gemporia we don’t ever stock anything above VS1 grade, as we don’t think they are worth the extra price.

And when it comes to prices in the trade, clarity has just as much impact on prices as colour. So that 4 carat G graded Diamond I mentioned earlier, which was $47,000 per carat if it was IF graded (so the second highest grade), would be $6,600 per carat if it was I1 graded.

What Difference Does This Make?

So taking both colour and clarity into account, our 4 carat Diamond, which to the eye would look virtually identical, can be reduced from $87,750 to $6,600 per carat – an immense saving! This is true of every size of Diamond - the only real difference is the price! For this reason, here at Gemporia, we always recommend G-H Colour, and I1-I2 Clarity.

With the budget left over by buying G-H, I1-I2 Diamonds, you always have the option of significantly increasing the size of your Diamond, or getting hold of a fancy cut gem. You could also think about getting 18K Gold or even Platinum to make your piece extra special.

I’m also going to quickly mention that there are ungraded Diamonds available on the market. Some of these Diamonds can sell for as little as $1 a carat! As you might imagine, their clarity is very, very poor. If you can’t get hold of the grading details for any Diamond you are buying, and the deal seems too good to be true, you may find yourself taking home Diamonds that are very nearly industrial grade. Always ask what grade you are getting!

We hope that has helped clarify things slightly. Find your perfect Diamond here.

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