Cut registry › Jewellery cuts › Trillion
Jewellery cuts · Fancy brilliant
The triangular brilliant.
Most trillion guides are about settings. This one is about the fact that two different stones share the name, and that the shape measures far better than it is given credit for.
The short version
A trillion cut diamond is a triangular brilliant, carrying either 31 facets with straight sides or 50 facets with convex sides depending on its intended use.
It is cut shallow, which is why it spreads further across the finger for its weight than almost any other shape.
Definition
The name is a contraction of triangle and brilliant, and it is used interchangeably with trilliant across the trade. The distinction that actually matters is not the spelling. It is that two different stones are sold under this name: an accent trillion with 31 facets and straight sides, and a centre-stone trillion with 50 facets and gently convex sides.
Anyone comparing trillion prices without knowing which they are looking at is comparing different things. Ask for the facet count. It is the single most useful question on this page.
The trillion’s usual career is as a matched pair flanking a centre stone in a three-stone ring, typically between 0.10 and 0.50 carats each. That is worth saying plainly rather than writing about it as though it were a mainstream solitaire, which it is not.
The three corners are the vulnerability. Modern trillions are almost never finished with true knife-edge points: the corners are slightly rounded or bruted to reduce the risk of chipping, and they still want prong protection.
Proportions
Commonly cited ranges against our measured reference stone. Note the depth figure: advice written for a round brilliant is actively wrong here.
| Measure | Commonly cited | Our reference stone | What it does |
|---|---|---|---|
| Length-to-width | 1.00 to 1.10 | 1.06 | An equilateral outline, give or take. |
| Depth | 32% to 48% | 50.7% | Genuinely shallow by design, and the reason it spreads. |
| Table | 50% to 65% | 56.6% | The flat top, as a share of the width. |
| Pavilion angle | not commonly published | 49.7° | Decides whether light returns or escapes. |
| Facets | 31 accent, 50 centre stone | 73 | Counted as facets that actually reach the surface. |
A trillion at 40% depth is not a shallow stone that has gone wrong. It is a trillion. Depth guidance written for round brilliants, which expects around 60%, will condemn every correctly cut trillion on the market. GIA issues no cut grade for the shape.
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 | 66.74% | 12.65% | 87.32 | 80.25 | 80.86 | −7.75 |
| Moissanite | 59.51% | 11.79% | 93.32 | 80.25 | 80.52 | −9.31 |
| Cubic zirconia | 72.81% | 14.32% | 92.95 | 80.25 | 84.31 | −7.46 |
| T57 standard, diamond | 92.28% | 1.88% | 78.85 | 71.82 | 88.61 | 0.00 |
Our reference trillion scores 80.86 Global against the standard’s 88.61, which places it third among the twenty-one jewellery cuts we measure in diamond. For a shape most guides treat as an accessory rather than a stone in its own right, that is a genuinely interesting result.
It returns 66.74% of entering light usefully and leaks 12.65%. Its fire reads 87.32, the second highest of the group, and at 73 active facets it scores 80.25 on scintillation against the standard’s 71.82.
It also reads 106.62 on the Index spread axis, among the highest we publish. That axis is derived from depth, so it is a statement about millimetres per carat rather than about outline area, and on a stone this shallow it is exactly the right measurement: a trillion buys its face-up size by being flat.
Variants
The two names are used interchangeably in the trade. The library carries two distinct geometries under them, so the question of whether it matters can be answered rather than argued.
| Geometry | Facets | Useful light | Leak | Fire | Global | What differs |
|---|---|---|---|---|---|---|
| Trillion on this page | 73 | 66.74% | 12.65% | 87.32 | 80.86 | The reference stone every other figure here describes. |
| Trilliant | 70 | 78.04% | 11.05% | 83.37 | 80.48 | The library’s other triangular brilliant: fewer facets, straighter sides, and it returns more light. |
They land close on Global and get there by opposite routes: the trilliant returns substantially more light, the trillion throws substantially more fire. If someone offers you a choice between the two words, this is what is actually behind it. The trilliant has its own page.
Against the standard
Light return. 92.28% for the round against 66.74% for the trillion, a Global gap of 7.75 points, which places it third of 21.
Sparkle character. 73 facets against 57, giving 80.25 on scintillation against 71.82, and 87.32 on fire against 78.85. A trillion throws bright, broad, angular flashes rather than the round’s fine pattern.
Face-up size. 106.62 on the spread axis, among the highest we publish. A shallow triangular outline covers a great deal of finger for its weight, and this is the main practical reason to choose one.
Durability. Three corners against a round’s none. Rounded or bruted tips plus prong protection make the difference between a durable stone and a chipped one.
Price. Generally less per carat than a comparable round.
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 trillion returns 59.51% for 80.52 Global, with fire at 93.32. A shallow shape with broad facets is a good showcase for moissanite’s dispersion, since the flashes are large enough to show the colour clearly.
In cubic zirconia it returns 72.81% for 84.31 Global, its strongest showing of the three materials.
Compare all three for this shape 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.
A trillion cut diamond is a triangular brilliant. The name contracts triangle and brilliant, and it is used interchangeably with trilliant. It carries either 31 facets with straight sides, in accent form, or 50 facets with gently convex sides when cut as a centre stone.
In practice the two words are used interchangeably across the trade. The distinction worth asking about is a different one: accent trillions carry 31 facets and straight sides, while centre-stone trillions carry 50 facets and convex sides. Those are genuinely different stones sold under the same name.
Either 31 or 50, depending on whether it is cut as an accent stone or a centre stone. Our reference trillion measures 73 facets that actually reach the surface, which is the count behind its scintillation figure of 80.25.
The three corners are the weak points, as they are on any pointed shape. Modern trillions are almost never finished with true knife-edge tips; the corners are slightly rounded or bruted to spread the stress. Even so they need prongs that cover each corner rather than sitting beside it.
Yes, and by a wide margin. A trillion is cut shallow, commonly between 32% and 48% depth, so far less of its weight sits below the table. Our reference trillion reads 106.62 on the Index spread axis, among the highest of the shapes we measure.
Around 32% to 48%. That is far shallower than any brilliant, and depth advice written for round diamonds does not transfer: applying a 60% expectation to a trillion would reject every correctly cut example on the market.
No. GIA issues cut grades for round brilliants only, so a trillion report carries symmetry and polish and nothing about light performance.
Better than their reputation suggests. In the 50-facet form our reference trillion scores 80.86 Global, third among the twenty-one jewellery cuts we measure in diamond. The practical constraint is availability rather than performance: most trillions on the market are cut as accents.
Generally yes, per carat, and noticeably so in accent sizes where they are produced in volume as matched pairs.
Because their main role is as matched side stones flanking a centre stone in a three-stone ring, typically at 0.10 to 0.50 carats each. A pair has to match in outline, depth and colour, so they are cut and sold together.
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 trillion 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.
80.25 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.