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The Ultimate Round Cut Diamond Buying Guide

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If you are shopping for jewelry featuring round diamonds, you are in good company.  Almost 75% of all diamond jewelry sold showcases round cut stones in their designs.  Popular, yet timeless, the round diamond is a style staple.  This article has the only 4 tips you need to know when buying a round diamond so you don’t waste your money. 

anatomy round brilliant Blue Nile
The anatomy of a round brilliant cut diamond as shown by Blue Nile.

The remarkable popularity of round cuts is no accident. In fact, round cut diamonds are special for several reasons. Most importantly, well-cut round diamonds boast mathematical precision in their faceting (the individual polished surfaces). This perfection creates optimal light return and intense sparkle, resulting in gems which impress in all lighting conditions.

14K Yellow Gold Alternating Pierced Diamond Choker Necklace by Brevani
Find this Necklace at James AllenJames Allen offers this necklace which features seven round brilliant cut diamonds.

History of Round Brilliant Diamond Cuts

The beauty of round diamonds has been known for centuries. However, the technology required to achieve the perfect proportions and symmetry required for such diamonds has only recently been available. Previous to the development of the necessary technology, round-ish diamonds from the nineteenth century are known as Old European Cuts (OEC) or Old Mine Cuts (OMC).

Old Mine, OEC, and Round Brilliant Comparison
Diagram comparing the faceting of OECs and OMCs to the modern Round Brilliant.

As you can see from the image above, cutters in the nineteenth century could not quite achieve the perfect roundness or symmetry necessary for their product to be called a true, round cut diamond. As a result of inconsistent faceting results, OEC and OMC diamonds lack the intense Brightness (white flashes), and Fire (colored flashes) characteristic of modern round brilliant cuts. 

The Birth of Round Brilliant Cut Diamonds

It was not until the twentieth century that specific proportions for a round cut diamond were laid out. Polish engineer Marcel Tolkowsky published a work in 1914 which provided proportions and angles which, he claimed, would maximize the beauty of a faceted diamond. It is from this baseline that the proportions which are now recognized for round brilliant cuts have emerged.

A tour of the round brilliant cut diamond’s facets.

So, what exactly is a round brilliant cut diamond? These stones feature 57 or 58 individual facets, depending on whether or not the cutter decided to shave off the point of the culet at the bottom of the stone. These facets are mostly kite and triangular shapes.

When grading round diamonds, The Gemological Institute of America (GIA) takes into account three factors regarding the face-up appearance of each stone: brightness, fire, and scintillation. As mentioned, a diamond’s brightness refers to the white flashes you see when looking at the stone. Fire describes the rainbow flashes. Finally, scintillation references the pattern created by the brightness and fire. Diamonds are the most beautiful when you have ample brightness and fire coupled with balanced scintillation. 

Round Diamonds and the 4C’s

Carat – When shopping for diamonds, round or not, consumers will see a great deal of information about manipulating the famous 4C’s to their advantage. For instance, if a shopper is looking for a big stone with lots of carat weight and is not too concerned with color or clarity, they will be told to find a stone whose 4C’s mirror these preferences. Conscientious shopping will allow you to wisely invest your money in stones which reflect your unique priorities. 

round diamond blue nile
Find this Diamond at Blue NIleThis round diamond sold by Blue Nile has a substantial carat weight of 1.5 ct. Its’ J-color and SI2 clarity grades help to keep the price under $7,000.

Color – The GIA grades the color of colorless diamonds on an alphabetical scale beginning with “D” as entirely colorless and most valuable. Considering color alone, prices decrease with each step down the scale.

GIA Color Grades for White Diamonds
This Normal Color Range Scale.

It is helpful to keep in mind that diamonds absorb color from their surroundings. If you set a round diamond in a yellow-metal setting, that stone may appear a full color grade lower than it actually is. Fortunately, the reverse is also true. If you want a very white diamond but have a restrictive budget, it makes sense to find a stone with a color grade in the Near-Colorless range and have that stone set in a white-metal mounting. Diamonds whose color is ranked beneath the Near-Colorless range are too yellow for this trick to work effectively.

Clarity – The GIA grades a diamond’s clarity on a scale with the following five categories: Flawless (F), Internally Flawless (IF), Very Very Slightly Included (VVS 1 – 2), Very Slightly Included (VS 1 – 2), Slightly Included (SI 1 – 2) and Included (I 1, 2 and 3). Like with Color, the lower the grade, the less valuable the stone. 

diamond clarity chart
GIA Clarity Grading Scale.

There are many articles which break down each of the subsections in the clarity grading scale. For most shoppers, the important distinction comes between SI1 and SI2. While there are some exceptions, generally speaking, SI1 graded stones or better lack eye-visible inclusions (impurities) while SI2 and lower stones may have eye-visible features. Eye-visible inclusions are defined as internal characteristics in the diamond which you can see without the aid of magnification. These characteristics might appear as dark spots, greyish cloudy regions, or white lines. 

For those wanting to make a financial investment in a superior stone, Flawless and Internally Flawless is the way to go.  However, you should understand that a Flawless stone and an SI1 stone lacking eye-visible inclusions are going to look exactly the same to the naked eye. They will, however, have drastically different price tags. It is perfectly reasonable to ask diamond sellers if a particular stone has eye-visible features. 

For stones that do have eye-visible inclusions, their size, location, and color are important factors in the overall beauty of the stone. You may not be bothered by a few tiny dots far off to one side of the stone. Alternatively, a large dark crystal in the center of the diamond may be unsightly. Inclusions in stones in the I-range are going to be noticeable. Because the inclusions are so severe, the durability of the diamond can be compromised. You won’t find I3 stones on the market because their poor clarity renders them too fragile to set in jewelry.

The SI1 diamond on the left offered by James Allen has a few darkish spots which are not visible without close scrutiny. The SI2 diamond on the right has black spots directly in its center which are harder to miss.

Cut – Finally, while you can manipulate the combination of Color, Clarity, and Carat to fit your unique preferences, a diamond’s Cut is different when it comes to rounds. As the beauty of round stones requires precision, any variance in their proportions and symmetry will noticeably detract from their appeal. One may compare this to non-round, fancy cuts, like ovals and hearts, whose proportions can vary widely. Thus, the GIA only issues a Cut grade for round diamonds where specific ratios are important. 

In total, the GIA employs five grades to describe the cut of a round diamond on their reports: Excellent (EX), Very Good (VG), Good (G), Fair (F), and Poor (P). As a diamond’s cut is so integral to its beauty, retailers like James Allen, Blue Nile, and Ritani simply do not offer stones whose cut grade is less than Good.

A comparison of a round cut diamond with a Cut grade of Excellent (left) with one that is poorly cut (right).

As you can see from the image above, the diamond that is well cut showcases regular, clean, and balanced lines. There are clearly defined light and dark regions and their patterns are perfectly symmetrical. Conversely, the poorly cut diamond seems chaotic, featuring no clear patterns for the eye to recognize. You see a mess which lacks visually interesting configurations and the eye wanders away. 

The Versatility of Round Diamonds

Part of the reason that round diamonds are so popular is that they can be incorporated into any design aesthetic. Rounds may be used as primary diamonds, set inside halos, or be flanked by additional stones. They are also a timeless option for solitaire rings or stud earrings. There are options featuring round diamonds regardless of your tastes and budget.

ZAC Zac Posen Vintage Three-Stone Diamond Engagement Ring in 14k White Gold Blue Nile
Find this Ring at Blue NileThis vintage-style design from Blue Nile features a round center diamond flanked by two pear-shaped stones and additional pave-set diamonds.
14K White Gold Contoured Twist Tension Set Engagement Ring James Allen
Find this Ring at James AllenFor those who are attracted to minimalist, ultra-modern designs, this tension-set diamond ring from James Allen is an elegant choice.
ZAC Zac Posen Art Deco Hexagon Halo Diamond Engagement Ring James Allen
Find this Ring at James AllenFor the individuals who prefer the bold geometry which characterizes Art Deco designs, this Blue Nile yellow gold ring checks all the right boxes.
Round Diamond Halo Stud Earrings Ritani
Find these Earrings at RitaniRitani offers these timeless, halo-set round diamond stud earrings.
14K Yellow Gold Graduated Diamond Necklace James Allen
Find this Necklace at James AllenDesigns with round diamonds don’t have to have a single, showstopping stone. This necklace from James Allen features graduating round diamonds for a classic look that can be dressed up or down.

Smart Shopping Tips for Buying A Round Diamond

When shopping for round diamonds (or any diamonds for that matter…), there are a few techniques which can be used to help you locate the best option which fits into your budget. 

Tip #1: Choose a round diamond with a “Good” cut

The first trick we have already touched on – smart juggling of the 4C’s. If you know which of the 4C’s matter the most to you, you can search for stones which best meet your needs and, thus, invest your dollars into exactly what you want. However, you now know that, when it comes to the Cut grade of a round diamond, it is wise to select stones which have, at the very least, a grade of Good. Although plentiful on the market, stones with lower cut grades will be noticeably dark and dull, lacking brightness, fire, and scintillation. 

Tip #2: Choose a round diamond that is slightly below your “magic” number

Another neat money-saving technique has to do with, what many in the trade call, “magic sizes”. This term describes how there are significant jumps in price-per-carat costs which occur at specific, round carat weights. By “round” weights, I mean numbers which are easy for people to wrap their minds around, like 0.25, 0.5, 1.0, and 1.5. If you know what size diamond you are looking for, choosing a stone which weighs slightly less than the nearest “magic size” may save you a significant amount of money. For instance, if you really want a 1.0-carat diamond, it makes sense to search for one which weighs 0.97 or 0.98 carats. Your eye won’t be able to tell that the diamond is 0.02 carats less than your target weight, but your wallet will.

Petite Solitaire Engagement Ring in 18k Yellow Gold Blue Nile

The diamond on the left weighs 1.03 carats. The diamond on the right weighs 0.96 carats. Can you tell the difference?

Tip #3: Decide whether you need to pay for perfection

You will notice a similar effect of price jump with each ladder separating the categories of the 4C’s. When it comes to the Cut grade, James Allen sells their most perfectly round diamonds as “True Hearts” stones. When shopping their site, you can filter for the True Hearts cut category. The site claims that only one percent of diamonds meet the criteria to be marketed in this way. Similarly, Blue Nile markets stones as “Astor Ideal” which they also claim represents less than 1% of all diamonds on the market. What you are paying for is perfection. However, the visible difference between True Hearts/Astor Ideal and Ideal diamonds may be extremely slight, and you can usually save money by going for a lower graded stone.

18K White Gold Bow-Tie Channel Set Diamond Engagement Ring James Allen
Find this Ring at James Allen18 kt white gold ring with 0.5 ct diamond featuring F color, VS1 clarity with a True Hearts rated cut grade from James Allen.

Tip #4: Fluorescence will save you money

Finally, you may be able to save money by selecting a round diamond which has some degree of fluorescence. Fluorescence describes a glow (usually blue as seen in about a third of natural diamonds) that results from exposure to ultraviolet light. The GIA grades fluorescence on a five-level scale: None, Faint, Medium, Strong, and Very Strong. Some sellers are overly concerned that fluorescent stones are less beautiful than non-fluorescent stones, especially in daylight where they are exposed to naturally occurring ultraviolet light. As a result, they may discount stones with strong fluorescence while charging a premium for non-fluorescent diamonds. 

While you may see some milky whiteness in Very Strongly fluorescent stones in daylight, this effect should not be apparent in any diamond ranked Medium or less. In fact, you should only be able to see that blue glow in a dark room illuminated with a black light. Seeking out diamonds with a Medium or Strong fluorescence grade from a dealer who discounts their fluorescent inventory may save you some money.

diamond fluorescence
A diagram showing examples of the five fluorescent grades as presented by Ritani.


When shopping for round diamonds, the sky is the limit.  Prioritize Cut quality with round diamonds and implement our other tips to help stay within your budget.  This timeless gemstone is as adaptable as it is alluring.  You can find stones in all sizes and can set them in any setting you like.