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.
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.
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.
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 →Last updated: 2026-07-16