Round Brilliant Cut Diamond Buying Guide

Buying a Diamond can be challenging, with lots of “information” out there but this guide will make things a lot clearer!

Whether you are buying for an engagement ring or piece of jewelry, you want to buy the best Round Brilliant Cut Diamond you can and that is what I will cover in detail.

First off, who am I to give this information? I’m Paul Haywood FGA DGA and I’m a fully qualified gemologist with over a decade’s worth of experience in the industry, 7 years of which were running my own online retailer.

Quick Summary

Don’t want to read the whole post? Don’t worry, I’ve summarized it for you below:

  • Color – If you want a colorless Diamond, then an F, G or H offers this without the premium of a D or E color stone
  • Clarity – A VS1 or VS2 Diamond won’t have any visible inclusions to the naked eye and you can get some very clean-looking SI1 stones, avoid I clarity Diamonds
  • Cut – always go for Diamonds with Very Good or Excellent Cut, Symmetry and Polish and avoid stones with thick or extra thick girdles
  • Fluorescence – not as big of an issue as made out to be, only a small number of Diamonds with very strong fluorescence will have an undesirable milky appearance
  • Reports – often called certificates, best to go for a Diamond with a report from a reputable gem lab such as the GIA or IGI

Round Brilliant Color

Color is one of the 4 C’s that are used to assess the quality of a Diamond and an important thing to consider when buying your Diamond.

If you are looking to buy a colorless Diamond, then you are going to want to look at stones that are graded between D and H as these are all colorless when viewed through the top of the stone (often called table-up).

An E Color Diamond Table Up
E Color Diamond
A G Color Diamond Table Up
G Color Diamond
An I Color Diamond Table Up
I Color Diamond

Most people only start to notice a hint of color in the stone at an I grade and as you move further along the scale, this tint becomes much more notable.

You may see people say that a H grade will have a tint of color but this is only seen when looking through the pavilion (bottom) of the stone, which is how color in Diamonds is graded but through the top of the stone, it will be colorless.

In terms of prices, D and E color Diamonds attract a premium as they are rarer but for those shopping to a budget, an F, G or H will get you a nice, colorless Diamond and it would take a trained Diamond grader to be able to tell the difference, especially when the stone it set.

If you are wondering what the difference is between D – G color Diamonds if they are all colorless? Simply, it is how ‘bright’ the stone is and this is hard to show on a screen.

Obviously, if you have the budget or just want a stone you can brag about, then go for a D Color Diamond.

Round Brilliant Clarity

The second of the 4 C’s is Clarity and another important aspect of buying a Diamond.

As with color, clarity is graded on a scale from Flawless to Included but the design of the round brilliant means that it can make inclusions look less obvious than they would in other styles of cut.

A VVS Clarity Diamond
A VVS Clarity Diamond
A VS Clarity Diamond
A VS Clarity Diamond
An SI Clarity Diamond
An SI Clarity Diamond

Higher-clarity Diamonds attract a premium, with many people often wanting a VVS clarity Diamond but without magnification and experience of looking at Diamonds, it is very difficult to tell the difference between a VVS and VS.

This is why I think that VS Diamonds offers the best option in terms of clarity, especially if you are working to a budget.

Good quality SI1 Diamonds are also worth considering depending on how noticeable the inclusion/s are and the location, if they are under the crown facets, then they are more difficult to see, especially when the stone is set.

I always recommend avoiding I clarity Diamonds as their inclusions not only affect the beauty of the stone but can also compromise its durability.

And as with color, if you have the budget or want a stone to really brag about, then go for a Flawless Diamond.

Top Tip: If you are browsing Diamonds online, remember that they are magnified and under optimal lighting and even though an inclusion may look big/obvious on the picture, that may not be the case when looking at the Diamond in person.

Round Brilliant Cut Quality

Arguably, Cut Quality is the most important of the 4 C’s and the one where you should go for the highest grade you can as the quality of the cut has a big impact on how much life and sparkle your Diamond has.

The GIA has 5 cut quality grades, which are:

  • Poor
  • Fair
  • Good
  • Very Good
  • Excellent
GIA Cut Scale

And I recommend buying a Diamond with a Very Good or Excellent cut grade as this increases the chances of your Diamond looking like you would expect a Diamond to look.

You also want to buy a Diamond with Very Good or Excellent Symmetry and Polish, a stone with an Excellent grade for all three might be referred to as a Triple X Diamond.

Round Brilliant Cut Diamond Proportions

When it comes to the quality of cut with a Diamond, there are 4 main proportions that you want to pay attention to, if you want to take a deeper dive when buying a Diamond.

1. Table Size and Crown Angle

Diamond cut proportions - table size
Diamond cut proportions - Crown Angle

I’ve put these two proportions together as the one usually affects the other and vice-versa.

The table size is the size of the main facet on the top of the stone and the crown angle is the angle of the facets between the girdle and the table and for Very Good and Excellent cut stones, they should be:

Table SizeCrown Angle
Very Good50 – 66%26.5° – 38.5°
Excellent52 – 62%31.5° – 36.5°

But why are these proportions so important?

Because they balance the amount of fire, which is how much light is dispersed by the crown facets (the rainbow colors that you see) and brilliance, which is how much light is returned to the eye.

Diamond cut proportions - ideal table size
Ideal table size: Good mix of fire and brilliance
Diamond cut proportions - large table
Large table: More brilliance but less fire
Diamond cut proportions - small table
Small table: More fire but less brilliance

2. Pavilion Angle

The next proportion that has a big impact on how good or bad a Diamond looks is the pavilion angle, which is the angle of the facets between the girdle and the culet (the point at the bottom of the stone).

Ideally, you want to buy a Diamond that has a pavilion angle between 39.8° – 42.4° for Very Good or 40.6° – 41.8° for Excellent.

But why is this proportion so important?

Diamond cut proportions - ideal pavilion angle
Ideal Pavilion Angle: Light reflected out of the top of the stone
Diamond cut proportions - shallow pavilion angle
Shallow Pavilion Angle: Light leaks out of the bottom of the stone
Diamond cut proportions - steep pavilion angle
Steep Pavilion Angle: Light leaks out of the pavilion of the stone

Because it impacts on the amount of light that is reflected within the stone back to the eye and Very Good and Excellent cut Diamonds aim to return the maximum amount of light.

If the pavilion angle is too shallow or steep, then it affects how the light is reflected and can result in dark areas or unwanted reflections in the stone, which aren’t ideal.

3. Girlde Thickness

Girdle thickness doesn’t have a huge impact on how your Diamond looks (unless you are looking at it from the side) but it can impact on a couple of other things.

  1. An Extremely Thin girdle is more likely to get chipped or damaged
  2. With Very Thick and Extremely Thick girdles, you are paying for additional carat weight but not getting a larger stone

Very Thin and Thick girdles are ok (they fall within the parameters for a Very Good cut grade) but I recommend going for a Thin, Medium or Slightly Thick girdle if possible.

Round Brilliant Carat

The weight of the Diamond you buy is going to depend on your budget but one thing to be aware of is that the weight of a Diamond doesn’t directly correlate to size.

And even though there are charts out there, such as my Round Brilliant Size to Weight chart, these should only be used as guides as the proportions vary from stone to stone, meaning two stones can have the same diameter but slightly different weights.

A D Color Diamond Table Up

1/4 Carat = 4.1mm

A D Color Diamond Table Up

1/2 Carat = 5.1mm

A D Color Diamond Table Up

1 Carat = 6.5mm

A D Color Diamond Table Up

2 Carat = 8.1mm

A D Color Diamond Table Up

3 Carat = 9.3mm

The images above aren’t to scale as this is very difficult to do with different sizes screens and resolutions!

But they can be useful for deciding what size Diamond you want, especially if you are buying a Round Brilliant Diamond for an engagement ring.

For many people, somewhere between 1/4 carat and 1 carat will be an ideal-sized Diamond that can be worn daily and one thing to remember is that the larger the diameter of the stone, the deeper it will be.


Possibly the most misunderstood (and sometimes mis-sold) aspect of Diamonds is fluorescence as for many years it has been seen as a bad thing and something to avoid.

But in reality, this simply isn’t the case as only a small number of Diamonds with very strong fluorescence impact on the look of the stone as it can give them a slightly milky appearance but this doesn’t happen with every Diamond that has very strong fluorescence (I’ve seen some stunning stones with very strong fluorescence).

And you will pay more for a Diamond with no fluorescence, assuming that all other factors are the same.

So don’t be put off by a Diamond that has little, medium or strong fluorescence as it won’t impact how the stone looks and can actually make your stone pop a little in strong sunlight!

Reports (Certificates)

GIA Lab Report

Most Diamonds for sale now come with reports but not all reports are the same.

Just to clear things up, Diamonds reports are often sold as certificates or certified Diamonds but they aren’t actually certificates, they are reports as there are differences between these two types of document.

The most popular gem lab for Diamond reports are the GIA (Gemological Insitute of America) as they are one of the leading authorities on Diamonds.

But there are other gem labs, such as IGI and HRD, that are also reputable gem labs and Diamonds with reports from these labs shouldn’t be ignored.

However, there are times when the documentation with a Diamond should cause you to run away and that is if the document says something like “Diamond Certificate” or “Certificate of Authenticity” as no reputable gem lab includes this wording on their documents.


I’ve covered everything you need to know in order to buy the right Round Brilliant Cut Diamond for you and this is the same whether you are buying and Natural or Lab-grown Diamond.

To summarize again, for the majority of buyers I would recommend buying a:

  • F, G or H color
  • VS1 – SI1 Clarity
  • Very Good or Excellent Cut Quality, Symmetry and Polish
  • A report from a reputable gem lab

If you have a very large budget or want the ultimate show-off Diamond, then go for a D Flawless or as close as you can get.

One thing I haven’t covered is price as Round Brilliant Cut prices move with the market as they aren’t affected by current fashions or trends like some other styles of cut and I track Diamond Prices monthly, if you are interested in that,

I'm Paul Haywood FGA DGA, the owner and founder of Haywoods Gems, I'm a fully qualified Gemmologist and Diamond Grader from the Gemmological Association of Great Britain.

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