Round Cut Diamond

Round Brilliant

Round cut diamond - sample image
sample image
Shape: Round
Also known as: Round Brilliant
Cutting style: Brilliant
Facets: 58 (57 if no culet)
L/W ratio: 1.00 - 1.02

Quick Intro

Round Brilliant is the ultimate classic and the most popular of all diamond shapes. Commonly used in engagement rings, it is designed to produce maximum fire, brilliance, and scintillation (sparkle). It has evolved over several hundred years and is the most researched and scientifically analyzed cut in the industry. Simple, timeless, and beautiful.

Round Diamond Size Chart (carat to mm)

The following is a chart of actual Round diamond sizes (from 0.25 to 10 carats) with their corresponding face-up dimensions in millimeters (length×width). This will give you an approximate idea of how big a stone of a certain weight looks or should look. The table is interactive, meaning you can click on any stone to view it in a diamond ring simulator.

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0.25 carat Round
4.09×4.09 mm
0.5 carat Round
5.16×5.16 mm
0.75 carat Round
5.91×5.91 mm
1 carat Round
6.5×6.5 mm
1.25 carat Round
7×7 mm
1.5 carat Round
7.44×7.44 mm
1.75 carat Round
7.83×7.83 mm
2 carat Round
8.19×8.19 mm
2.25 carat Round
8.52×8.52 mm
2.5 carat Round
8.82×8.82 mm
2.75 carat Round
9.11×9.11 mm
3 carat Round
9.37×9.37 mm
3.25 carat Round
9.63×9.63 mm
3.5 carat Round
9.87×9.87 mm
3.75 carat Round
10.1×10.1 mm
4 carat Round
10.32×10.32 mm
4.25 carat Round
10.53×10.53 mm
4.5 carat Round
10.73×10.73 mm
4.75 carat Round
10.93×10.93 mm
5 carat Round
11.11×11.11 mm
5.25 carat Round
11.3×11.3 mm
5.5 carat Round
11.47×11.47 mm
5.75 carat Round
11.64×11.64 mm
6 carat Round
11.81×11.81 mm
6.25 carat Round
11.97×11.97 mm
6.5 carat Round
12.13×12.13 mm
6.75 carat Round
12.28×12.28 mm
7 carat Round
12.43×12.43 mm
7.25 carat Round
12.58×12.58 mm
7.5 carat Round
12.72×12.72 mm
7.75 carat Round
12.86×12.86 mm
8 carat Round
13×13 mm
8.25 carat Round
13.13×13.13 mm
8.5 carat Round
13.27×13.27 mm
8.75 carat Round
13.39×13.39 mm
9 carat Round
13.52×13.52 mm
9.25 carat Round
13.64×13.64 mm
9.5 carat Round
13.77×13.77 mm
9.75 carat Round
13.89×13.89 mm
10 carat Round
14×14 mm
Length-to-width ratio: 1

Round Cut Size Comparison With Other Shapes

For a given weight, Rounds typically look larger when viewed from the top than Asschers, Princesses, Cushions, Hearts, Emeralds, and Radiants (in that order). Conversely, they look smaller compared to Ovals, Pears, Trillions, and Marquises. Sizewise, they are roughly in the middle. They are, however, the sparkliest of them all. They are also the most expensive, but for good reason. In order to cut a round diamond to perfection (for maximum brilliance and sparkle) more rough is lost than for any other shape.

Here is the size comparison of Round Brilliant with diamonds of all other shapes. The percentages show average face-up size difference:

The main reason why a certain shape faces-up smaller or larger is depth. For example, Princess cut diamonds are deeper, meaning that carat for carat, they will face up smaller. On average, Rounds will have approximately 9% more top surface area than Princesses. On the other hand, they will be approximately 15% smaller than a shallow cut like Marquise.

Buying Guide For Round Brilliants

Round brilliants are very good at masking inclusions and color, which means you can go quite low in terms of clarity and color grades without sacrificing the appearance. Cut, on the other hand, which determines the fire and brilliance should always be of the highest possible grade (Excellent for GIA or Ideal for AGS).

Here is what to look for and what to avoid when buying round diamonds:

Look for:
  • Color: J or higher [depends on a setting]
  • Clarity: SI or better [explain]
  • Cut: Excellent (GIA) or Ideal (AGS)
  • Cut parameters:
    • Depth: 58% - 62.5%
    • Table: 53% - 58%
    • Polish/Symmetry: Good or better
    • Length-to-width ratio: 1.00 - 1.02
  • Diamonds certified by GIA or AGS [explain]
  • Eye-clean

Watch out for:
  • Inclusions visible to the naked eye
  • Extremely thin or extremely thick girdle
  • Fair or Poor symmetry
  • Strong blue fluorescence [explain]
  • Diamonds without GIA or AGS certification [explain]

Price: How To Choose For Best Value?

Diamond prices vary greatly. The value of a diamond is based on the combination of its unique characteristics - the 4Cs (Cut, Color, Clarity, and Carat). The key is to choose the combination that will have a reducing effect on price and little to no effect on appearance. The following is a quick overview of the best value recommendations for Round diamonds:

With round diamonds you don't skimp on cut, period. That is, if you want a sparkly and fiery stone, which you probably do. Cut has to be of the highest possible grade. Not Good or even Very Good, but only Excellent (for GIA) or Ideal (for AGS).

This is where it gets interesting. Brilliants are great at masking color so you can go safely down the color scale without ever noticing any difference. How far down depends on the setting or whether or not you plan to have side-stones (the size of side-stones is also important). If you're planning to go with platinum setting and solitaire stone, then the color should be at least J. For a yellow gold setting you can go even lower to K. When diamonds are mounted you will be hard pressed to tell the difference. Your wallet, on the other hand, will know the difference.

Brilliants are also good at masking inclusions, which again means you can go down on clarity scale without anyone noticing. SI1 or even SI2 clarity offer fantastic value for money, however, you must make sure the diamond is eye clean. Being clean to the eye simply means that any imperfections are not detectable with the unaided naked eye. If you're buying online and are unsure, just ask the vendor.

Did you know that diamond prices jump quite dramatically at full and half carat marks. You can save money by going below these marks. Up to 10%, the size difference will be practically unnoticeable. Use this website to compare different sizes and see how far down you're comfortable going.

Where To Buy Round Diamonds?

Online vendors will always offer better prices compared to bricks & mortar stores, simply because of the overhead. They also have enormous selections and with the new technology you can easily inspect every diamond really up-close in 360-degree view. Nowadays, it's easy and safe to shop online. So it's simple: for best value, buy online. Here are the most recommended online retailers (click here to learn why):

Compare Round with another diamond

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carat vs. length* width* depth*
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Color Recommendation For Round Diamonds

Round Brilliants don't show color as much as other cuts, so you can go quite a few steps down on the color scale without noticing any difference. The choice of color also depends on a setting:

Solitaire Small side-stones Substantial side-stones
White gold/Platinum J+ I+ same as side-stones+
Yellow gold K+ J+ same as side-stones+
e.g. pave setting e.g. three-stone setting
Note: If side-stones are of any significant size (like in three-stone settings), you should at least match the color of the center stone with the color of the side stones, otherwise the center stone might look out of place (a bit "off-white").

For best value, go with the minimum recommended color for a particular type of setting. Color variations between J graded and higher colored Round cuts are so slight that it's almost impossible to tell the difference, especially when diamonds are mounted. The difference in price, however, can be quite considerable.

Clarity Recommendation For Round Diamonds

Round Brilliants are great at masking inclusions, so you can go relatively low on clarity scale without sacrificing the appearance, as long as the diamond is eye-clean. SI1 or SI2 clarity offers great value for money.

Note: You can always go lower in clarity, but it's going to get increasingly difficult to find an eye-clean Round below the minimum recommended SI2 grade.

For best value, go with the lowest clarity possible that is still eye-clean. If a diamond is eye-clean, then it doesn't really matter, if it's flawless or SI2. It will look the same, provided all other characteristics are the same.
About Diamond Clarity
Diamond clarity refers to the presence and visual appearance of the flaws inside a diamond (called inclusions) or on its surface (called blemishes). Clarity tells you to what degree these imperfections are present.

The amount of inclusions and blemishes is directly correlated to a diamond's value. Fewer imperfections mean higher price and vice versa.

Gemological laboratories grade diamond clarity as Flawless (FL), Internally Flawless (IF), Very Very Slightly Included (VVS1,VVS2), Very Slightly Included (VS1,VS2), Slightly Included (SI1,SI2), and Included (I1,I2,I3).

GIA and AGS Certified Diamonds

Professional and unbiased assessment of a diamond's characteristics is stated on a diamond grading report, commonly referred to as a certificate. Certificate, while not 100% reliable, is essential in determining a diamond's value.

The standard for diamond grading is pretty much set by GIA - Gemological Institute of America. They are the most reputable and consistent lab in the industry. AGS (American Gemological Society) is not far behind.

If a diamond is not certified by GIA or AGS, you can be pretty much certain that you are looking at lesser quality than indicated. This puts you in a bad position of not knowing the true diamond characteristics, which almost always results in overpaying. That is why a certificate from a well-respected grading lab is so important.

The bottom line: Make sure to always buy a diamond certified by either GIA or AGS. That's the only way of truly getting the quality you expect.

Diamonds with Blue Fluorescence

Blue fluorescence can have a positive, negative, or zero effect on a diamond. Diamonds in the lower color range (H or lower) can benefit from it, as it can make them look whiter, more colorless. On the other hand, strong fluorescence can cause a stone (especially in the higher color range D-G) to appear hazy or milky under certain light conditions. One of the biggest benefits of fluorescent diamonds is that they generally cost less.

GIA grades fluorescence as None, Faint, Medium, Strong, and Very Strong.

Faint fluorescence will have zero effect on color and overall appearance. Fluorescence of this type is not an issue and shouldn't be a purchasing factor.

Medium fluorescence will in most cases have zero to very small influence on color and overall appearance, however, colorless diamonds can sometimes exhibit negative effects and should be examined in different light conditions before purchasing.

Strong/Very Strong fluorescence requires caution. Generally, it's not a good idea to buy a colorless diamond with Strong/Very Strong fluorescence. As for lower color diamonds, even they can sometimes look hazy with strong fluorescence, so never buy a stone with this type of fluorescence without careful visual inspection.

If you're interested in fluorescent diamonds that have been carefully examined and do not display any negative effects of fluorescence, I recommend Brian Gavin's Blue Diamonds. Those are definitely top of the line and a great value.

Diamonds Without GIA or AGS Certificates

The problem with diamond grading labs other than GIA or AGS is that they are looser and more inconsistent in their grading standards. A GIA color H is an IGI color G and an EGL/HRD color F. The same goes for clarity.

While it's true that IGI, EGL, and HRD diamonds are sold at a discount, you can be certain that the same stones would cost less, if they would be certified by GIA or AGS. Why? Because they would get lower grades and thus lower price. Lower than discounted IGI, EGL, and HRD stones with higher grades.

Diamond merchants use IGI, EGL, HRD, and alike to maximize their profits. They know they can sell diamonds with inflated grades for more, even if they're sold at a substantial discounts. Some merchants also use their in-house certification, usually for the sole purpose of increasing their profits. These kinds of certificates are meaningless.
The bottom line: If you don't want to overpay and want to know exactly what kind of quality you're getting, then avoid diamonds without GIA or AGS certification.

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