Buyer’s Guide to Round Diamonds

Close your eyes and picture a diamond. You are picturing a round brilliant. This iconic diamond cut symbolizes millions of marriages, adorns millions of ears, and paves countless inches of gold.

What is the difference between a round diamond and a round brilliant diamond? While other kinds of round diamonds are technically possible, like a round rose cut diamond or an antique Old European cut, the modern round brilliant diamond is not only the most popular round diamond on the market, it’s the most popular diamond cut of all time.

The round brilliant diamond cut, with its 58 facets, pointed culet, and optimized proportions is the culmination of hundreds of years of perfecting the art of diamond cutting. Yes, the round brilliant is that good.


The History of Round Brilliant Diamonds

Diamond faceting began in the 15th century when it was first discovered that diamonds could be polished by their own dust. Before that, diamond rough and polished crystals were the only way to wear this gem. Faceting unlocked the potential for sparkle. Once cutters discovered the beauty of polished diamonds, they kept innovating, starting by polishing crystals, cutting off the top of the crystal to create a table cut and then step cuts. In the 16th century faceted rose cuts were developed, followed by the cushion shape old mine cut.

Mazarins, the first brilliant cuts with more facets to maximize brilliance, were introduced in the middle of the 17th century. Then the industrial revolution in the late 19th century transformed diamond cutting. New steam-powered bruting machines and motorized saws allowed cutters to shape diamonds like never before: the round diamond was born. The Old European cut and English round cut had 58 facets, the same as round brilliants today.

Over the decades, cutters adjusted the proportions and angles to improve light performance.

In 1919, a young Belgian student studying match in London, Marcel Tolkowsky, wrote Diamond Design, his thesis on the ideal proportions for round brilliant diamonds. Although his calculations omitted the girdle and needed to be adjusted, his work became the foundation for the modern round brilliant and the ideal diamond proportions still prized today.

Why We Love Round Diamonds

Brilliance. Fire. Scintillation. Nothing dances with light like a round brilliant diamond. These unrivalled optics are due to the symmetry and proportions that create optimum reflection, refraction, and scintillation. The round brilliant has the best light performance of any diamond cut, with the most light that returns to the eye.

A round brilliant diamond in the sunlight will throw reflections and rainbows across the room.

The pure circular silhouette of the round brilliant has inspired many ring styles, from the halo to the solitaire, and the three stone. That’s another reason why the round brilliant diamond cut is the most popular choice for engagement rings.

The angles and proportions of round diamonds have been studied the most by diamond grading laboratories. That means that the cutting standards for the round brilliant are higher in general than for any other cut. The round brilliant is the only diamond cut with a cut grade on its GIA diamond grading report. Because GIA is the world’s most important diamond grading laboratory, it is very influential in the industry. Cutters want to make sure that the diamonds they craft receive high marks for cut from the GIA so cutting standards for the round brilliant have improved overall.

There’s one more reason why the round brilliant diamond cut is the most popular choice for engagement rings: it’s the most common cut so there is more choice available. You can select from thousands of options in every color, clarity, and carat weight.

There is one drawback to choosing a round brilliant diamond: high demand means that they are the most expensive diamond cut in most sizes. A round brilliant sells for more per carat than any fancy shape. It also looks smaller than many other fancy shapes.

How to Buy Round Diamonds

The brilliance of most rounds makes them bright, so you don’t have to buy the top color grade to get a beautiful diamond. You also are less likely to see inclusions because of all that sparkle, so you don’t need to buy a flawless gem to have a beautiful diamond either. But what you definitely don't want to skimp on is cut: look for an excellent cut and your diamond will live up to the potential of the round brilliant to dazzle with brilliance.

The best way to buy a round brilliant diamond is to buy it loose and then set it into a ring.

Buying a loose diamond will give you more control over its quality. Choose a diamond with a diamond grading report from GIA or AGS, the world’s most respected diamond grading laboratories, to make sure that the quality has been independently verified from an accurate and impartial third party.

If you choose a round diamond with an excellent cut grade from GIA, popularly known as an ideal cut, you’re sure to own a beautiful and well-crafted diamond. You can also buy diamond cut to an even higher standard: a round brilliant hearts and arrows diamond which demonstrates superior light performance when evaluated with a viewer that confirms the maximum amount of light is being returned back to your eye.

What ROSI Recommends

When you are shopping online for a round brilliant diamond, there are thousands and thousands available: too many for anyone to individually review one by one. That’s why we created ROSI, an artificial intelligence personal shopping tool powered by IBM’s Watson: to sort through all the round brilliant diamonds available on the market to find the best balance of quality and value for your budget. Thanks to ROSI, you can find the best round brilliant diamond for your budget in one single step.

ROSI generally recommends a color of H and clarity of VS2 for round diamonds. This will give you a diamond that looks colorless with no inclusions visible to the naked eye. The money you save can be invested in a larger size diamond and a better cut. ROSI recommends excellent cut, symmetry and polish for a diamond that sparkles beautifully.

Round Brilliant Quality Checklist

  • Color: H
  • Clarity: VS2
  • Cut: Excellent
  • Symmetry: Excellent
  • Polish: Excellent
  • Depth: 58%-63%
  • Table: 53%-62%
  • Fluorescence: None to Faint
  • Comments: No chips!

There’s one final step to making sure that you’ve found the right round brilliant diamond. No matter where you found your diamond, you can compare your diamond by putting the GIA report number into ROSI. In a few seconds, you’ll see if artificial intelligence can find you a better diamond value. You may find a higher-rated diamond at the same price or a similar stone for a lower price. If not and your diamond passes the A.I. Challenge, you know you are really getting a great deal.

Round Brilliant vs Oval Shape Diamonds vs Cushion Cut Diamonds

The two diamond shapes that are most similar to a round brilliant diamond are the oval shape diamond and the cushion cut diamond.

The oval shape diamond is less brilliant than the round brilliant but its elongated silhouette and shallower depth means it looks much larger on your finger than a round brilliant the same weight. In addition, oval shapes sell for less per carat for the same quality and size.

Cushion cut diamonds are similar in size to the round brilliant and are the only other diamond cut that will display the hearts and arrows pattern in a light-performance viewer. A hearts-and-arrows cushion like RockHer’s Cushion Brilliant designed by master cutter Brian Gavin, is a great way to get the precision cutting and high light performance of a hearts and arrows cut for less per carat than a hearts and arrows round brilliant.

Best Round Diamond Engagement Ring Styles

Our customers’ favorite setting for round diamonds is a simple solitaire diamond band engagement ring. Delicate micropave halo engagement rings are also popular. Recently, we’ve seen more brides interested in unique halo engagement rings that have a more custom look. Simple diamond solitaire engagement rings are an eternal classic that never goes out of style, just like the round brilliant. Popular three stone styles feature three round diamonds or round with tapered baguettes on the side.

You’d be surprised how far your money can go shopping for a round diamond engagement ring online.

Solitaire with Pave Band


Halo Engagement Ring


Unique Halo


Three Round Diamonds


Tapered Baguette

Please upgrade your browser to access
We built RockHer on the latest technologies. That means works best with the following browsers. Please upgrade to one of these browsers for the best experience.