Round Brilliant Cut Engagement Rings: A Buyer's Guide for Canadians

A round brilliant is a circular diamond (or moissanite) cut with 57 or 58 facets arranged to return as much light as possible. It is the most popular engagement ring shape and the only diamond shape that gets an overall cut grade on a GIA report. For the most sparkle, choose Excellent or Very Good cut.

Most people picture a round stone when they think "engagement ring," and there's a good reason for that. The round brilliant has been refined for well over a century with one goal in mind: sparkle. It suits every setting style, it hides small inclusions and a little colour better than step cuts do, and it doesn't date. It also costs more per carat than most other shapes, which is why it pays to know exactly what you're buying. This guide covers what makes a good round, where you can save money without anyone noticing, and how to set it.

What is a round brilliant cut?

A round brilliant has a flat table on top, a sloped crown with 32 facets, and a deeper pavilion underneath with 24 more. According to GIA, the crown is made up of 8 bezel facets, 8 star facets and 16 upper halves, and the pavilion has 16 lower halves and 8 mains. Add the table and you have 57 facets. A tiny flat point at the bottom, called a culet, makes it 58.

Round diamonds existed long before the modern cut, but GIA credits a Boston cutter, Henry Morse, with making consistently round stones practical. His bruting machine of 1873 and his work on measuring facet angles led to the American cut, the forerunner of today's round brilliant. Modern rounds are cut with automated equipment to precise proportions, which is part of why quality is so consistent at the top end.

Why is the round brilliant the most popular engagement ring shape?

GIA, citing The Knot, says round brilliants make up nearly one third of diamonds sold for engagement rings. A few practical reasons sit behind that number:

• Sparkle. The facet pattern is designed to return light. Few shapes match a well-cut round for brightness.
• Forgiveness. The busy facet pattern masks small inclusions and faint colour better than step cuts like the emerald or Asscher.
• Versatility. A round looks at home in a plain solitaire, a halo, a vintage milgrain setting or a modern bezel.
• No points or corners. There's nothing sharp to chip, so it's one of the easier shapes to wear every day.

If you're still choosing between shapes, our guides to oval cut and cushion cut engagement rings cover the two shapes people most often compare with a round.

What cut grade should you buy for a round diamond?

This is the one decision we'd ask you not to compromise on. GIA grades round brilliants on a five-step scale: Excellent, Very Good, Good, Fair and Poor. It's the only shape that gets an overall cut grade on a GIA report. Fancy shapes like oval, pear and marquise get polish and symmetry grades but no cut grade.

The GIA cut grade looks at seven things: brightness, fire, scintillation, weight ratio, durability, polish and symmetry. The overall grade can't be higher than the lowest of the first five, so a stone with great brightness but a thick, heavy girdle won't get Excellent.

GIA cut grade	What you'll see	Our take
Excellent	Maximum brightness and fire	Our default recommendation for a centre stone
Very Good	Very close to Excellent to most eyes	Often the best value
Good	Noticeably less lively, especially in dim light	Fine for small side stones, not a centre stone
Fair / Poor	Dull or glassy, with dark areas	Avoid for an engagement ring

You'll also hear "triple Excellent" or "3X," which means Excellent cut, polish and symmetry. It's a nice shorthand, but it isn't a separate grade.

A practical tip from GIA that we agree with: look at the stone in different lighting, not just under jewellery-store spotlights. Daylight by a window and ordinary indoor light tell you far more about how it will look on the hand.

Does a round diamond need a high colour and clarity grade?

Usually not as high as people think, because the round's sparkle does a lot of masking. Cut comes first, then spend what's left on colour and clarity.

Colour

GIA describes G to H as a budget-friendly near-colourless range. Your metal choice matters here too. In yellow or rose gold, a slightly warmer stone looks perfectly at home, while a very icy D to F stone set in yellow gold picks up some warmth from the metal anyway. If you're set on white gold and a large stone, colour becomes more visible as size goes up, so it's worth stepping up a grade or two at 3 carats and above. Our comparison of white, yellow and rose gold covers how each metal changes the look.

Clarity

GIA notes that most VS2 and higher diamonds have no inclusions visible to the eye, and some SI1 stones don't either. That makes VS2 and well-chosen SI1 rounds the sweet spot for value. Flawless and internally flawless stones are rare and priced accordingly, and you won't see the difference without a loupe.

For the full picture of how the four grades trade off against each other, read our 4Cs guide.

How big does a 1 carat round diamond look?

A well-cut 1 carat round measures roughly 6.4 to 6.5 mm across. Carat is a weight, not a size, so a badly cut stone can carry extra weight in a thick girdle or a deep pavilion and look smaller face-up than a lighter stone with better proportions. That's another reason to put cut first.

GIA also points out that prices often jump at "magic sizes" like 0.50, 1.00 and 1.50 carats. A 0.90 to 0.98 carat stone can look almost identical to a 1.00 carat on the hand and cost noticeably less. If you're shopping around a round number, ask to see stones just below it.

Moissanite is usually sold by millimetre size rather than carat, since it's lighter than diamond for the same dimensions. A 6.5 mm round moissanite has roughly the face-up size of a 1 carat diamond. Our moissanite vs. lab diamond guide explains the other differences.

What is the best setting for a round engagement ring?

Four prongs or six prongs

Four prongs show more of the stone and can make a round look very slightly square. Six prongs hold the stone more securely and keep the outline looking perfectly round, at the cost of covering a little more of it. GIA's suggestion is four prongs for smaller stones and six for larger ones, which matches what we see at the bench. The Raina, our round cut solitaire, is a classic example of the clean look, and you can browse more in our solitaire collection.

Halo and hidden halo

A halo of small diamonds around the centre stone adds sparkle and makes the round look larger. A hidden halo tucks that row of stones under the centre, so it only shows from the side. The Bella, our round cut hidden halo ring, is a good example. See our halo engagement rings for more.

Bezel

A rim of metal surrounds the stone. GIA calls bezels the most protective and smoothest setting. They're a good choice if you work with your hands, and the trade-off is a little less light entering from the sides. Our article on bezel-set jewellery goes into the details.

Three-stone and toi et moi

A round centre flanked by two side stones, or paired with a second stone of a different shape, gives you a ring with more personality. Our guide to 3-stone engagement rings covers side stone options.

Is a round diamond more expensive than other shapes?

Generally, yes. Rounds tend to cost more per carat than fancy shapes of similar quality, largely because so many buyers want them. If budget is tight and you love the look of a round, you have good options: choose a lab-grown diamond or moissanite, buy just under a magic size, add a halo for visual size, or go one colour grade lower in yellow or rose gold. Our custom engagement ring cost guide breaks down where the money goes.

How to check a round diamond's grading report

• Cut grade. Excellent or Very Good. If a report on a round doesn't show a cut grade, ask why.
• Polish and symmetry. Very Good or better.
• Girdle. Avoid "extremely thin" girdles, which GIA warns are more prone to chipping.
• Fluorescence. Usually not a problem, but ask to see the stone if it's strong.
• The lab. GIA and IGI are the names you'll see most in Canada. Our IGI vs GIA guide explains how they compare.

Frequently asked questions

How many facets does a round brilliant diamond have?

57 or 58. The crown has 33 including the table, the pavilion has 24, and an optional culet at the bottom adds the 58th.

What is the best cut grade for a round diamond?

Excellent gives the most brightness and fire. Very Good is often the better value and looks very similar to most people. Avoid Good or lower for a centre stone.

How big is a 1 carat round diamond in mm?

About 6.4 to 6.5 mm across when well cut. A poorly cut 1 carat stone can measure smaller because extra weight is hidden in the girdle or pavilion.

Is a round diamond better than an oval?

Neither is better. A round has more sparkle and gets a GIA cut grade. An oval looks larger for its carat weight and lengthens the finger, but can show a bow-tie.

Should a round diamond have four or six prongs?

Four prongs show more of the stone and suit smaller rounds. Six prongs are more secure, keep the outline perfectly round and suit larger stones.

What colour and clarity are best for a round engagement ring?

For good value, G to H colour and VS2 or an eye-clean SI1 clarity. Consider a higher colour grade for stones of 3 carats or more in white gold.