Round Brilliant
The round brilliant is the standard modern diamond cut: a circular outline faceted specifically to maximise the return of light back to the eye.
Abbreviated as: RBC
Also known as: Brilliant cut, Round brilliant cut
| Culet | Usually none, or a minute point |
|---|---|
| Outline | Circular |
| Faceting | Modern brilliant |
| Crown angle | Typically 34–35° |
| Facet count | 57 or 58 (with culet) |
| Typical use | Any diamond jewellery |
| Availability | Most widely available cut |
What defines the cut
The round brilliant is a circular outline cut with 57 or 58 facets (including the culet), arranged in a pattern mathematically optimised for light return rather than for preserving rough weight. Modern proportions trace back to Marcel Tolkowsky's 1919 analysis of angle and depth combinations that maximise brightness and fire, refined further through the 20th century by labs including GIA into the "Excellent" / "Ideal" cut-grade systems used today.
Visual characteristics
Cut well, a round brilliant shows strong, evenly distributed brilliance (white light return), fire (spectral flashes) and scintillation (sparkle on movement). Proportions matter more here than for almost any other shape — table size, crown and pavilion angles, and symmetry are all independently graded by major labs because small deviations measurably reduce light performance.
Buying considerations
- Cut grade matters more for round brilliants than for any fancy shape — prioritise it over marginal upgrades in colour or clarity.
- A well-cut round hides colour and inclusions better than a poorly cut one of higher paper grade.
- Face-up size is well correlated with carat weight for this shape, unlike elongated shapes — a 1ct round is a fairly reliable ~6.4mm.
Jewellery suitability
The round brilliant works in essentially every setting style — prong solitaires, bezels, halos, three-stone and pavé designs all suit it, which is a large part of why it remains the best-selling diamond shape.
Terminology
"Brilliant cut" on its own, without a shape qualifier, is usually shorthand for round brilliant — but the same faceting style (as opposed to step-cut faceting) is applied to fancy shapes too (oval brilliant, pear brilliant, cushion brilliant), so it's worth confirming which is meant.
Trade notes
Round brilliants are the most liquid diamond shape in the trade — easiest to match for pairs, easiest to resell, and the shape with the deepest published pricing data (e.g. Rapaport). Certificate cut-grade fields (GIA Excellent/Very Good/Good, etc.) are specific to round brilliants; fancy shapes are not cut-graded on the same scale by GIA.
Frequently asked questions
- Is a round brilliant always a diamond?
- No — the term describes the facet arrangement, not the material; round brilliant sapphires, spinels and other stones are common.
- Why do round diamonds cost more per carat than fancy shapes?
- More rough is lost in cutting a round brilliant than most fancy shapes, and demand is highest for round, so both supply and demand push the price per carat up relative to shapes like pear, marquise or radiant of comparable quality.
Compared with
Related cuts
An Old European Cut is an antique round brilliant with a small table, high crown, large visible culet and circular (rather than cushion-like) outline — the direct ancestor of the modern round brilliant.
An Old Mine Cut is an antique brilliant style with a squarish-to-rounded cushion outline, a high crown, small table, and usually a visible culet, cut by hand before mechanised, symmetry-optimised faceting existed.
A cushion is a square or rectangular shape with rounded corners and sides, giving it a soft, pillow-like outline; the modern cushion brilliant applies contemporary brilliant faceting to that outline.
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