Its character
The most studied cut in the trade, and the only one with a grading scale devoted entirely to its proportions. Angles are held within fractions of a degree, because a round shows deviation more readily than any other shape. It carries the highest cost per carat in rough, since a round yields less finished weight than a shape that follows the crystal.
Where the round cut comes from
The round brilliant grew out of the old European cut of the late nineteenth century. Two changes made it: the bruting machine, which let cutters turn a truly circular girdle, and Marcel Tolkowsky's 1919 study Diamond Design, which worked out crown and pavilion angles for a balance of brightness and fire.
Modern rounds have smaller tables, sharper culets and more precise angles than Tolkowsky's model, and optical research since the 1990s has made the round the only shape with a full laboratory cut grade. That grade is why rounds are the easiest shape to compare on paper, and also why they are the most price-transparent.
How a round is faceted
A standard round brilliant has 57 facets, or 58 if a culet is polished: 33 on the crown (table, 8 bezels, 8 stars and 16 upper girdle facets) and 24 or 25 on the pavilion (8 mains and 16 lower girdle facets). The lower girdle facets are what break light into the fine, needle-like sparkle rounds are known for.
Because every facet repeats around the stone eight times, small errors in angle or alignment show up as uneven patterns. A precisely cut round can show a hearts-and-arrows pattern in a viewer, which is a sign of optical symmetry, not a grade in itself.
Round cut proportions
Ranges most well-cut round stones fall within. They narrow the field; they do not replace seeing the stone.
| Measure | Typical range | Why it matters |
|---|---|---|
| Table | 54 – 58% | Wider tables trade fire for brightness. |
| Depth | 59 – 62.5% | Deeper stones face up smaller for their weight. |
| Crown angle | 34 – 35° | Read together with the pavilion angle. |
| Pavilion angle | 40.6 – 41° | Too steep or too shallow leaks light. |
| Girdle | Thin to slightly thick | Extremely thin girdles chip. |
| Culet | None or very small | A large culet shows as a dot face-up. |
What to look for in a round diamond
Because the round has a published cut standard, it is the easiest shape to compare on paper: table and depth appear on the report, and an Excellent or Ideal cut grade narrows the field quickly. What the figures cannot show is how the stone behaves in real light, so two rounds with the same grades are still worth seeing side by side. It suits almost any setting, and it is the safest choice where a stone may be reset later.
- Cut grade first
- Excellent (GIA) or Excellent/Ideal (IGI) removes most poorly proportioned stones. Below Very Good, the loss of brightness is usually visible.
- Angles, not only percentages
- Two stones with identical table and depth can perform differently. Crown and pavilion angles are printed on the report and are worth reading together.
- Light performance by eye
- Reflector images or a video in daylight show contrast and leakage that no grade prints. Compare two graded stones side by side where you can.
- Fluorescence
- Strong blue fluorescence occasionally makes a stone look hazy. It is listed on the report, but whether it matters has to be judged on the stone.
Setting a round
A round works in almost every setting: four prongs show more of the stone, six prongs protect it better, and a bezel suits an active lifestyle. It is also the easiest shape to reset later, because mounts for rounds are made in every size.
Round size by carat weight
Approximate face-up size at a typical round ratio and depth, drawn to scale. Select a weight to see natural stock in that band.
5 mm. Every silhouette is drawn to this scale, at typical proportions.
- Natural round diamonds, 0.25–0.49 ct, about 4.1 mm face up
- Natural round diamonds, 0.50–0.74 ct, about 5.1 mm face up
- Natural round diamonds, 0.75–0.99 ct, about 5.8 mm face up
- Natural round diamonds, 1.00–1.49 ct, about 6.4 mm face up
- Natural round diamonds, 1.50–1.99 ct, about 7.3 mm face up
- Natural round diamonds, 2.00–2.99 ct, about 8.1 mm face up
- Natural round diamonds, 3.00 ct and above, about 9.3 mm face up
Diamond carat guide: every shape, price milestones and choosing a weight
Terms used on this page
Each one is defined in full, with what a report prints for it, in the glossary.
- Brilliant cut
- A faceting style built from triangular and kite-shaped facets radiating from the centre.
- Cut grade
- An overall verdict on how well a round brilliant has been cut — issued for rounds only.
- Crown angle
- The angle between the girdle plane and the sloping crown facets.
- Pavilion angle
- The angle of the pavilion facets below the girdle — the most sensitive number on the stone.
- Hearts and Arrows
- A pattern of eight arrows from above and eight hearts from below, shown by a special viewer on exceptionally symmetrical rounds.
- Light leakage
- Light that enters the stone and escapes through the bottom or side instead of returning to the eye.
Round cut questions
What buyers ask most often before choosing a round diamond.
How many facets does a round brilliant diamond have?
A standard round brilliant has 57 facets, or 58 when the culet is polished as a facet: 33 on the crown and 24 or 25 on the pavilion.
What is the best depth and table for a round diamond?
Most well-performing rounds fall between about 59 and 62.5 percent depth with a 54 to 58 percent table, but proportions should be read together with the crown and pavilion angles and the report's cut grade rather than on their own.
Why are round diamonds more expensive per carat?
Cutting a round from rough loses more weight than most fancy shapes, and demand for rounds is the highest in the market. Both push the price per carat up compared with an otherwise similar fancy shape.