Round Cut Diamond: A Buying Guide

Round cut diamond.

The most popular diamond shape is the round brilliant cut. Carefully refined over nearly 100 years to maximize light return and sparkle, this shape has proven the test of time as a sought after choice. Almost three quarters of all diamond engagement rings feature a round brilliant diamond. Due to the mechanics of its shape, the round diamond is generally superior to fancy diamond shapes at the proper reflection of light, maximizing potential brightness. Virtually all round diamonds are brilliant cut, meaning they have 58 facets (57 when there is no culet).

Round Cut Diamond

Round cut diamond.

Clean, classic, versatile and with more fire and brilliance than any other shape, it would be difficult to persuade anyone against this choice, as proven by the fact that it accounts for more than half of all diamonds sold today. For men wishing to surprise their ladies and unsure of what they might like, one could hardly go wrong here.

Round Cut Diamond Buying Guide

Also referred to as: TOLKOWSKY IDEAL CUT

Round Cut Diamond Quick Guide

Unique Features
Considered to be of ideal proportions to maximise brilliance and fire
58 (57 if culet pointed)
L/W Ratio
1.00 - 1.02
17th Century Mazarin
Expert Tip
Most brilliant and popular of all shapes; versatile and classic

Round Cut Diamond Ring

Round Cut Diamond Ring

Round cut diamond ring.

Round Cut Diamond Features

Round Cut Diamond Features

Round cut diamond features.

The round brilliant cut is the most popular diamond shape, accounting for more than half of all diamonds sold today. Although developed in Europe, the round brilliant is sometimes referred to as the American Ideal Cut.

With 58 facets divided amongst its crown, girdle and pavilion and a typical ratio between 1.00 and 1.02, it yields maximum shine as the cut naturally follows the rough diamond crystal.

The round brilliant is the most researched cut in the industry; for over a century, diamond cutters have used advanced scientific theories of light reflection and precise mathematical calculations to optimize its fire and brilliance.

Round Cut Diamond Expert Guide

The round brilliant is the most versatile of all cuts both in terms of style and value. With more fire and brilliance than any other shape, this offers the ideal balance between cut, color and clarity grades and budget.

For a bachelor unsure of what might please his lady, it is hard to go wrong with this classic choice.

Round diamonds cost more on a per carat basis than fancy shapes for two reasons; the demand for round diamonds is very high, and the yield is relatively low. Because more of the rough diamond is lost in the cutting of a round diamond, the cost of each carat retained is higher. A typical round diamond (for example; a 1.00 carat, F color, VS2 clarity, Excellent cut) may cost 25-35% more than a similar fancy shape.

The round diamond began to rise in popularity in 1919 with the publication of Marcel Tolkowsky's thesis "Diamond Design: A Study of the Reflection and Refraction of Light in Diamond". Tolkowsky's work described the ideal proportions of a round cut diamond for maximizing light return (or brilliance) and dispersion (or fire). The original Tolkowsky specifications (53% table, 59.3% depth, 34.50 degree crown angle, visible culet) have since been modified as the cut mechanics for round diamonds have perfected over time. These theoretical advancements, as well as advancements in technology (such as the use of lasers in diamond cutting), have been adopted by diamond manufacturers to produce the incredibly brilliant cuts we see today in well cut round diamonds.

The pavilion depth and angle are also significant for maximum radiance and scintillation. The pavilion is the cone-shaped part of the diamond from girdle to base. The depth percentage of the pavilion is calculated as the percentage of the pavilion depth relative to the girdle diameter. The pavilion has main facets and lower half facets that reflect fiery sparkles of light when cut to ideal proportions. A shallow pavilion angle can result in a "fish eye" effect, while a pavilion angle that is too steep can result in your diamond looking like a "nail head", with a dark centre.

Poorly cut diamonds with "nail head" and "fish eye" defects:

Poorly Cut Diamonds With Nail Head & Fish Eye Defects

Poorly cut diamonds with "nail head" and "fish eye" defects.

Round Cut Diamond - Cut Guide

The quality of the cut is the most important factor in maximizing the brilliance and fire, meaning it greatly affects the appearance of a diamond.

According to the GIA, round brilliant diamond cut quality is graded on a scale from Excellent to Poor. The closer a diamond to excellent cut parameters, the more brilliance and sparkle it exhibits.

As mentioned, an excellent cut diamond may cost up to 35% more than any other diamond shape with similar characteristics.

The table below serves as a general guideline for evaluating the cut of a round diamond. GIA takes these and other factors into consideration when assigning a cut grade:

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Round Cut Diamond Excellent Very Good Good Fair Poor

Depth refers to the distance between the culet and the table when a diamond is viewed from the side.

The depth % of a diamond is calculated by dividing the depth of the diamond by the width of the diamond. So, if a diamond is 3 mm in depth, and 4.5 mm in width, its depth % is 66.7.

The lower the depth %, the larger a diamond of a given carat weight will appear when viewed from above (since more of the diamond's size is in its width vs. in its depth).

Depth % is incorporated in the cut grade of a diamond. For this reason, when purchasing a diamond, use the cut grade first (since it balances multiple measurements, not just depth %). Once two diamonds of equal cut are being compared, consider depth % as a further refinement.

Learn more about the anatomy of a diamond.

59 - 62.3 58 - 58.9 or 62.4 - 63.5 57.5 - 57.9 or 63.6 - 64.1 56.5 - 57.4 or 64.2 - 65 <56.5 or >65

The table is the uppermost, flat surface of a diamond, which runs parallel to the plane of the girdle.

The table % of a diamond is calculated by dividing the width of the table facet by the width of the diamond. So, if the table facet is 3 mm across, and the diamond is 4.5 mm wide, its table % is 66.7.

Table % is incorporated in the cut grade of a diamond. For this reason, when purchasing a diamond, use the cut grade first (since it balances multiple measurements, not just table %). Once two diamonds of equal cut are being compared, consider table % as a further refinement.

Learn more about the anatomy of a diamond.

53 - 58 52 - 53 or 58 - 60 51 or 61 - 64 50 or 65 - 69 <50 or >69

A diamond's symmetry is the arrangement, size, and shaping of diamond's facets. The facets are the flat planes that run along the surfaces of the diamond. Symmetry is angles and lines that form the placement of the facets. Nowadays, symmetry is completely controlled by the manufacturing process. Machines very carefully cut diamonds to produce the most accurate shapes. However, at times the diamond cutter will leave a symmetry imperfection in the diamond in order to prevent a different inclusion from showing in the finished diamond. Symmetry is a subset of the diamond's cut grade.

Learn more about diamond symmetry.

Very good to excellent Good to excellent Good to excellent Fair to Excellent Poor to Excellent

The term "polish" refers to the overall condition of the surfaces of a finished diamond. A rating is assigned based on the amount of polishing lines that are visible. These polishing lines are caused by very small diamond crystals which are embedded in the polishing wheels used by diamond cutters to polish the surface of the diamond after cutting. Diamond polish is important because it can affect the degree to which light is able to pass through a diamond, rendering it more or less brilliant. Diamonds that are laboratory certified with a good, very good, or excellent polish rating are the most desirable. Diamonds that have poor polish will be less brilliant and not as desirable or valuable. Reputable jewellers diamonds are graded after examining the diamond facet by facet.

Learn more about diamond polish.

Very good to excellent Good to excellent Good to excellent Fair to Excellent Poor to Excellent

Refers to the number of degrees between the plane of the table and the bezel facets. The crown angle will determine how much light is reflected into the pavilion at an angle that will allow it to be reflected back up through the crown (where the observer can perceive it).

Learn more about the anatomy of a diamond.

34 - 34.9 32.1 - 33.9 or 35 - 35.5 30.1 - 32 or 36 - 37.9 29 - 30 or 38 - 40.5 <29 or >40.5

The entire portion of the diamond that sits below the girdle. The pavilion usually constitutes the bulk of a diamond's carat weight and consists of the pavilion facets and culet. Pavilion height may be expressed in millimeters, or as a percentage of a diamond's diameter.

Learn more about the anatomy of a diamond.

42.8 - 43.2 42 - 42.7 or 43.3 - 43.9 41 - 41.9 or 44 - 45.5 39 - 40.9 or 45.6 - 48 <39 or >48

The girdle is the outer edge of the diamond, where the crown (top) meets the pavilion (bottom).

A girdle may be faceted (a series of tiny polished sides going around the diamond), bruted (a single continuous unpolished surface going round the diamond; no longer common), or polished (a bruted girdle that has been polished smooth). Whether a girdle is faceted, bruted, or polished usually has no impact on the appearance or value of the diamond.

The girdle is described according to its width. Often, the width of the girdle varies at different points around the diamond, and is quoted in a range designating the thinnest and thickest point along the girdle (e.g. "Thin - Medium" means the diamond's girdle varies in width from thin at the narrowest point to medium at the widest point).

Learn more about the anatomy of a diamond.

Thin - Slightly Thick Very Thin - Slightly Thick Very Thin - Thick Very Thin - Very Thick Ex. Thin - Ex. Thick

The culet (pronounced cue-let) is the small area at the bottom of a diamond's pavilion. The culet can be a point or a very small facet sitting parallel to the table.

The culet size as determined by the GIA, is shown using the following scale:

None, Very Small, Small, Medium, Slightly Large, Large, Very Large.

Any culet size of Medium or smaller will be invisible to the naked eye, and have no negative impact on a diamond's appearance. However, if a culet is Slightly Large or larger, it may allow light entering from the crown to pass straight through the culet facet, reducing the diamond's brilliance. This may also make the culet appear as an inclusion, or create a dead area on the diamond where the light is escaping through the bottom.

Learn more about the anatomy of a diamond.

None Very Small Small Medium > Medium

The length to width (L/W) ratio is calculated by dividing a diamond's length (the longer measure) by its width (the shorter measure that runs perpendicular to length).

For example, an Oval Cut diamond that is 5.00 mm in length and 3.3 mm in width will have a L/W ratio of 1.50 (5.00/3.33). A perfectly round or square diamond will have a length to width ratio of 1.00, but many will be off slightly since they are often not perfectly cut. Any L/W ratio of 1.05 or less will appear perfectly round or square to the naked eye.

L/W ratio is more commonly used in fancy shapes. There is no "ideal" L/W ratio in a fancy shape diamond. What is important is what looks pleasing to you.

1.00 - 1.01 1.00 - 1.01 1.00 - 1.01 1.02 > 1.02

Round diamond cut guide

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Round Diamond Cut

Round diamond cut.

Round Cut Diamond Ratio

Round diamond length to width ratio.

Round Cut Diamond - Color Guide

Evaluating color in round cut diamonds is subjective. Keep in mind that many customers may actually prefer the ever so slightly warmer colors of a G-H diamond over the cool colorlessness of a D-F diamond. In fact, most of the premium in price associated with round diamonds at the higher end of the color scale is driven by supply and demand; customers want the D-F color grades, and are willing to pay a premium to get them. In a world without diamond color grading, the price premium for higher grades would be much lower, as the actual differences in color are difficult to perceive.

Since round cut diamonds reflect more light than any other diamond shape. they tend to mask yellowish tints in a diamond. That is why evaluating colour in a round cut diamond is quite subjective. Some people may prefer slightly warmer colours such as G-H while others buy only colourless D-F diamonds. The color chart below provides a general guide for evaluating color in round diamonds:

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Round Cut Diamond Excellent Very Good Good Fair Poor
< .50 ct. D - G H - I J - K L - M > M
.51-1.0 ct. D - G H - I J - K L - M > M
1.0-2.0 ct. D - F G - H I - J K - L > L
> 2.0 ct. D - F G H I - J > J

Fluorescence refers to a diamond's tendency to emit a soft colored glow when subjected to ultraviolet light. Roughly 30% of diamonds fluoresce to some degree.

Colorless (D-F) fluorescent diamonds sell at up to a 15% discount since the fluorescence is perceived as a defect, even though the visible effects of Faint to Medium fluorescence are perceptible only to a gemologist using a special UV light source.

Because the fluorescent glow is usually blue (which is the complementary color to yellow) fluorescence can make diamonds of I-M color appear up to one grade whiter. For this reason, I-M diamonds tend to sell at a slight premium when they possess Medium to Very Strong fluorescence.

Exercise caution in purchasing a diamond with Strong fluorescence in D-F color diamonds or Very Strong fluorescence in G-H color diamonds (which do not possess enough body color to offset the higher degree of fluorescence).

Learn more about diamond fluorescence.

None Faint - Med Strong Very Strong Very Strong

Round diamond color guide.

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Round Cut Diamond Color

Round cut diamond color.

Round Cut Diamond - Clarity Guide

Like color, evaluating clarity in round diamonds is subjective. GIA provides excellent help with their clarity grades. Still, it is important to understand that each customer will have a unique standard for clarity. Some may be perfectly comfortable with an inclusion as long as they cannot easily see it. Others may insist on a more technically flawless appearance.

The GIA grades clarity of round cut diamonds on a scale from FL to I3, where FL means a flawless diamond and I3 indicates a heavily included diamond.

For round cut diamonds, like for any other shape, the most important is to determine if the gemstone is eye-clean. In other words, you should feel comfortable to buy a diamond which inclusions are not visible without magnification. In case you still prefer flawless diamonds, be ready to pay a premium price. The clarity chart below provides a general guide for evaluating clarity in round diamonds:

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Round Cut Diamond Excellent Very Good Good Fair Poor
< .50 ct. FL - VS2 SI1 - SI2 I1 I2 > I2
.51-1.0 ct. FL - VS1 VS2 - SI1 SI2 I1 - I2 > I2
1.0-2.0 ct. FL - VVS2 VS1 - VS2 SI1 - SI2 I1 > I1
> 2.0 ct. FL - VVS2 VS1 - VS2 SI1 SI2 > SI2

Round diamond clarity guide.

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Round Cut Diamond Clarity

Round cut diamond clarity.

Round Cut Diamond History & Background

The origins of the round brilliant cut can be traced back to the middle of the 17th century when diamond cutters began using more refined and complex ways of cutting diamonds. The early brilliant cuts were known as Mazarins, after their designer Cardinal Mazarin, who made the first cross-cut diamond in 1650.

Through a series of gradual transformations and developments over the course of the 18th century, the Mazarins gave birth to the Portuguese Peruzzi, "old mine," or "old European cut" in the 1700s.

It was not until 1919 that the early modern round brilliant was created; at the time it was referred to as the Tolkowsky cut named after its creator, Russian mathematician and diamond enthusiast Marcel Tolkowsky.

Round Cut Diamond History

Round cut diamond history.

Learn more about what you need to know in our ultimate buying guide, if you're thinking of buying a round cut diamond. We break it all down from pricing, other shapes comparison and engagement ring setting choices.