Round Brilliant Diamond

The round brilliant is the most popular diamond shape, accounting for roughly 75% of all diamonds sold. Its 58 facets (57 without the culet) are mathematically optimized to maximize light return, fire, and scintillation.

Is a round brilliant diamond a good choice?

Round Brilliant diamonds are the most brilliant of all shapes with 58 facets. They're the most popular diamond shape on the market. Here are the trade-offs.

Why people love it

+Unmatched brilliance and fire among all diamond shapes
+Most standardized cut grading, making it easier to compare stones
+Works beautifully in virtually every setting style
+Hides inclusions and slight color better than most other shapes
+Strong resale value due to universal demand

Things to know

−Commands the highest price per carat of any shape
−Higher cutting waste drives up cost compared to other shapes
−Very common, so it can be harder to stand out with a unique look
−Can appear smaller than elongated shapes of the same carat weight

How big is a round brilliant diamond? (MM to carat)

A 1-carat round brilliant diamond measures approximately 6.5 mm. Here are the most common sizes from 0.25 ct to 5 ct.

Carat Weight	Size (mm)
0.25 ct	4.0 mm
0.33 ct	4.4 mm
0.5 ct	5.0 mm
0.75 ct	5.75 mm
1 ct	6.5 mm
1.25 ct	6.8 mm
1.5 ct	7.3 mm
2 ct	8.0 mm
2.5 ct	8.7 mm
3 ct	9.1 mm
4 ct	10.25 mm
5 ct	11.0 mm

View full round brilliant size chart → with all sizes from melee to 5+ carats.

How to buy a round brilliant diamond

•Prioritize cut quality above all other Cs. A well-cut 0.90ct will outperform a poorly-cut 1.10ct.
•Look for GIA Excellent or AGS Ideal cut grades for maximum light performance
•Consider going one color grade lower (e.g., H instead of G) in yellow gold settings where slight warmth is masked
•SI1 clarity is often the sweet spot. Inclusions are typically invisible to the naked eye.
•Buying just under popular carat thresholds (0.90 instead of 1.00) can save 10-20% with no visible size difference
•Ask for an ASET or Idealscope image to verify light performance beyond the lab report

What makes a round brilliant diamond unique?

The round brilliant cut was perfected by Marcel Tolkowsky in 1919, who used mathematical calculations to determine the ideal proportions for maximum light performance. His work established the foundation for modern diamond cutting, and the round brilliant remains the benchmark against which all other shapes are measured. Because the round brilliant has been so extensively studied, its cut grading is the most standardized in the industry. GIA, AGS, and other labs provide cut grades exclusively for round brilliants, making it easier for buyers to compare stones objectively. This standardization also means pricing is more transparent. Round brilliants follow well-established Rapaport pricing guides more closely than any other shape. From a manufacturing standpoint, round brilliants produce the most rough diamond waste, typically losing 50-60% of the original crystal. This high waste factor, combined with overwhelming demand, is the primary reason rounds command a premium over all other shapes. Despite the cost, the round brilliant's unmatched brilliance and versatility in virtually any setting style make it the default choice for engagement rings worldwide.

How much does a round brilliant diamond cost?

Round Brilliant diamonds are priced at highest of all shapes. the benchmark for diamond pricing.. Price depends on carat weight, color, clarity, and cut quality. For a personalized estimate, use our diamond price estimator.

Estimate round brilliant diamond price →

How does the round brilliant compare?

Round vs Oval Diamond→

Technical Specifications

Facets: 58
Brilliance: exceptional
L:W Ratio: 1.0:1 (perfect circle)

Diamond Buying Guide·All Diamond Shapes·Price Estimator·Round Brilliant Size Chart

Last updated: 2026-08-12

At a Glance

Price vs Round: Highest of all shapes. The benchmark for diamond pricing.
Popularity: Most popular (approximately 75% of all diamonds sold)
Sparkle: exceptional

Best For

engagement ringssolitaire settingsstud earringstennis braceletsany setting style

Setting Ideas

Solitaire (the classic choice that lets the stone's brilliance speak for itself)
Six-prong, Tiffany-style (the industry standard for round brilliants)
Halo. Adds perceived size and extra sparkle around the center stone.
Bezel. Provides maximum protection while maintaining a modern look.
Pave band. Complements the round's brilliance with additional sparkle.
Three-stone. Round center flanked by trillions, pears, or smaller rounds.

Related Shapes

Frequently asked questions

Is a round brilliant diamond a good choice?

Yes. Round brilliant is the most popular diamond shape for good reason. Its 58 facets deliver unmatched brilliance and fire, and it works in virtually every setting style. The trade-off is price: rounds command the highest cost per carat and can look slightly smaller face-up than elongated shapes of the same weight.

How big is a 1-carat round brilliant diamond?

A 1-carat round brilliant measures approximately 6.5 mm in diameter. Round brilliants are perfectly circular, so a single diameter measurement describes the face-up size.

How much does a round brilliant diamond cost?

Round brilliants are the most expensive shape per carat. They serve as the benchmark for diamond pricing across the industry. Expect to pay more for a round than any fancy shape of equal carat weight, color, and clarity.

What is the best setting for a round brilliant diamond?

A solitaire with a six-prong Tiffany-style setting is the classic choice and lets the stone's brilliance take center stage. Halo and pave band settings add perceived size and extra sparkle, while a bezel offers maximum protection for active wearers.

Why are round diamonds the most expensive?

Round brilliants lose 50 to 60% of the original rough crystal during cutting, far more than most fancy shapes. Combined with overwhelming demand and the only standardized cut grades in the industry, that high waste factor drives prices above every other shape.