Cut registry › Jewellery cuts › Octagon
Jewellery cuts · Step cut
Eight equal sides.
An octagon is what you get when a square step cut stops having corners to worry about. It is the most robust step cut we measure, and the steadiest as the hand moves.
The short version
An octagon cut diamond is a step cut with eight equal sides and facets arranged in flat parallel tiers, giving a regular octagonal outline.
It is the step-cut family’s answer to the durability problem: with eight shallow corners instead of four sharp ones, there is no single vulnerable point.
Definition
The octagon sits between the carré and the round in outline. Take a square step cut, cut all four corners deeply enough, and you arrive at a regular octagon. An asscher is the halfway house, with corners cut but the square still dominant.
Its facets run in tiers parallel to each of the eight sides, so the reflection pattern is denser and more even than a four-sided step cut can manage. What you lose is the long, sweeping hall-of-mirrors flash that an emerald cut gives, because no single facet is very long.
It is uncommon in diamond and more familiar in coloured stones, where the even outline suits a bezel and the tiers show body colour well.
Proportions
Trade description on the left, our measured reference stone on the right. There is no standardised proportion set for an octagon cut.
| Measure | Commonly cited | Our reference stone | What it does |
|---|---|---|---|
| Outline | regular octagon | regular octagon | Eight equal sides. |
| Length-to-width | 1.00 | 1.00 | Equilateral by definition. |
| Depth | not standardised | 61.0% | Comparable to other step cuts. |
| Table | not standardised | 60.0% | The flat top, as a share of the width. |
| Pavilion angle | not standardised | 50.2° | Shallow, and the figures below reflect it. |
| Facets | varies with tier count | 49 | Counted as facets that actually reach the surface. |
No laboratory issues a cut grade for an octagon, and reports normally describe it as an octagonal step cut. It is one of the few shapes here with no meaningful durability caveat.
Light
Measured on the census that runs on every cut on this site: 3,200 rays face-up, 2,200 at 20° tilt, on exact facet geometry, against T57 as the standard.
| Material | Useful light | Leak | Fire | Scintillation | Global | vs the standard |
|---|---|---|---|---|---|---|
| Diamond | 71.24% | 17.59% | 76.47 | 66.34 | 79.91 | −8.69 |
| Moissanite | 66.97% | 19.75% | 93.96 | 66.34 | 82.17 | −7.65 |
| Cubic zirconia | 75.84% | 16.35% | 79.95 | 66.34 | 82.26 | −9.52 |
| T57 standard, diamond | 92.28% | 1.88% | 78.85 | 71.82 | 88.61 | 0.00 |
The octagon returns 71.24% of entering light usefully for 79.91 Global against the standard’s 88.61, and leaks 17.59%.
Its standout figure is tilt. It holds 97.00 of its face-up return at a 20° tilt, against the round brilliant standard’s 90.41 and against the asscher’s much weaker figure. Among the step cuts we measure it is the steadiest by a clear margin, which is the practical opposite of the complaint asscher owners make.
It carries 49 active facets for 66.34 on scintillation, below the standard’s 71.82, with fire at 76.47. Fewer, more even returns rather than a dense flash pattern.
Where the light is: useful return across the face
Five equal bands across the stone. The octagon returns 68.7% at the centre against 65.6% at the edges, against the round-brilliant control’s 99.1% and 98.1%. An eight-sided outline distributes light more evenly than a four-sided one, which is most of the reason it holds up as the stone moves.
Against the standard
Light return. 71.24% against the standard’s 92.28%, for a Global gap of 8.69 points.
Movement. 97.00 against 90.41, and the octagon wins. It is one of very few cuts on this site that holds its return under tilt better than a round brilliant does.
Sparkle. 66.34 against 71.82, on 49 facets against 57. Fewer flashes, and broader ones.
Durability. Eight shallow corners rather than four sharp ones, so no protective setting is required. This is the octagon’s clearest practical advantage over a carré or a princess.
Availability. Uncommon in diamond. Easier to find, and more at home, in coloured stones.
The baseline for all of this is the round brilliant itself. Its facet plan is set out in the anatomy of a round brilliant, and the measured standard we compare against is T57, the stone Tolkowsky published in 1919.
Materials
In moissanite the octagon returns 66.97% for 82.17 Global with fire at 93.96.
In cubic zirconia it returns 75.84% for 82.26 Global.
The shape is most often seen in coloured gems, where the even tiers read against a body colour. Turn one in the Index.
Trade-offs
Questions
The questions buyers actually ask, answered in full. Where the answer is ours to prove, the figure is measured on the Index; where it is an established gemological fact, it is stated as one.
An octagon cut diamond is a step cut with eight equal sides and facets arranged in flat parallel tiers around each side. It is what a square step cut becomes when all four corners are cut deeply enough, and it has no single vulnerable point.
How far the corners are cut. An asscher is a square step cut with its corners cut off but the square still dominant. An octagon takes that further, to eight equal sides. The octagon is the more robust of the two and, on our census, holds its light far better under tilt: 97.00 against the asscher’s much lower figure.
Yes, and they are the most robust step cut we measure. Eight shallow corners spread the stress that four sharp ones would concentrate, so an octagon needs no protective setting, unlike a carré or a princess.
It returns 71.24% of entering light against the standard’s 92.28%, for 79.91 Global against 88.61. It beats the standard on one term that matters in wear: it holds 97.00 of its return at a 20 degree tilt against the round brilliant’s 90.41.
Less than a brilliant and less than most step cuts here: 66.34 on scintillation against the standard’s 71.82, on 49 measured facets. It produces fewer and broader returns, distributed very evenly across the face.
No. GIA issues cut grades for round brilliants only, and an octagon will normally be described on a report as an octagonal step cut.
More often in coloured stones than in diamond. The even outline suits a bezel setting and the tiers show body colour well, so it is a favourite in aquamarine, tourmaline and similar material. In diamond it is uncommon.
Higher than a brilliant would. Step facets are open planes with nothing to break up the view into the stone, so inclusions show more readily than in a brilliant of the same size.
Next
See the whole set on the jewellery cuts index, or the measured house and historic cuts in the cut registry.
Method
Monte-Carlo on exact facet geometry: 3,200 rays face-up plus 2,200 at 20° tilt, cosine-weighted from a 7° near-vertical cone. Useful light is what exits through the crown within 64° of vertical. The same protocol runs on every cut on this site, so the figures are comparable to each other.
They measure our reference geometry for the shape at the proportions listed above, not an average of stones on the market. A octagon cut to different proportions will read differently. Treat them as a like-for-like comparison between shapes, not as a grade for any individual stone.
Engine estimates, ±2 points, not lab-certified grades. We do not publish the Index symmetry axis on these pages: it scores facet regularity within each pavilion family, which is meaningful for a round brilliant and misleading for a shape whose pavilion is deliberately irregular.
66.34 here against the standard’s 71.82. The term is 100(1−e−n/45) on the count of facets that actually reach the surface, so it is a pure function of facet count and nothing else.