Its character
Cut shallow, so it spreads wide for its weight and sits low. Sides may be straight or slightly convex. Most often specified as a matched pair flanking a centre stone, which means symmetry between the two matters as much as the grade of either.
Where the trillion cut comes from
Triangular diamonds have been cut for centuries, often to make use of flat, triangular rough. The trilliant name was trademarked by the Henry Meyer Diamond Company of New York in the 1960s, and trillion and trilliant are now used generally for triangular brilliants.
The shape became established as a side stone in three-stone rings, where a matched pair frames a larger centre stone.
How a trillion is faceted
Trillions vary more than most shapes. Brilliant-style trillions have around 31 to 50 facets, and the sides may be straight or slightly curved. Curved sides are common on solitaires and straight sides on side stones.
They are cut shallow, so they cover a lot of surface for their weight. The three corners are the thin, exposed parts of the stone.
Trillion cut proportions
Ranges most well-cut trillion stones fall within. They narrow the field; they do not replace seeing the stone.
| Measure | Typical range | Why it matters |
|---|---|---|
| Table | Varies widely | Read the measurements rather than a single figure. |
| Depth | Shallow for side stones | Solitaires are usually cut deeper to hold light. |
| Length to width | 1.00 – 1.10 | An even triangle is the usual goal. |
| Girdle | Thin to medium | Very thin corners chip. |
| Culet | None | |
| Cut grade | Not graded | Neither GIA nor IGI assigns an overall cut grade to this shape, so these are trade ranges rather than a standard. |
What to look for in a trillion diamond
Check that the three sides match in length and that the corners are not cut too thin, since those are the points most at risk. The shallow cut means a trillion faces up large for its weight, which is exactly why it works so well beside a centre stone. As a solitaire it makes a modern statement, but it needs a protective setting.
- Equal sides
- All three sides should be the same length and all three corners the same angle.
- Matched pairs
- For side stones, the two trillions should match in size, outline, colour and brightness. A matched pair matters more than the grade of either stone.
- Windowing
- Very shallow trillions can look glassy in the centre. Check that the stone stays bright face-up.
- Corners
- Look for chips or very thin girdle at each point before setting.
Setting a trillion
As side stones, trillions sit on either side of a round, oval, cushion or emerald cut. As a centre stone, a bezel or a three-prong setting with V-prongs protects the corners.
Trillion size by carat weight
Approximate face-up size at a typical trillion 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 trillion diamonds, 0.25–0.49 ct, about 4.6 mm face up
- Natural trillion diamonds, 0.50–0.74 ct, about 5.8 mm face up
- Natural trillion diamonds, 0.75–0.99 ct, about 6.6 mm face up
- Natural trillion diamonds, 1.00–1.49 ct, about 7.3 mm face up
- Natural trillion diamonds, 1.50–1.99 ct, about 8.4 mm face up
- Natural trillion diamonds, 2.00–2.99 ct, about 9.2 mm face up
- Natural trillion diamonds, 3.00 ct and above, about 10.5 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.
- Spread
- How large a stone looks from above, relative to what its carat weight would suggest.
- Window
- A see-through patch in the middle of the stone where light passes straight out of the bottom.
- Parcel
- A group of stones of similar quality sold together rather than individually.
- Chip
- A small shallow break at the girdle, a point or the culet.
- Girdle thickness
- How thick the band at the stone's widest point is, graded Extremely Thin to Extremely Thick.
Trillion cut questions
What buyers ask most often before choosing a trillion diamond.
What is the difference between a trillion and a trilliant?
Trilliant began as a trademark for a specific triangular cut. Today both names are used for triangular brilliant-cut diamonds, and the difference is mostly in usage rather than in the stone.
Are trillion diamonds good as side stones?
Yes. They are cut shallow, so they cover a lot of surface for their weight, and their shape leads the eye toward the centre stone. Matching the two stones is the most important consideration.
Can a trillion be used as a centre stone?
Yes, usually with slightly curved sides and a deeper cut to hold light. It needs a protective setting because the corners are exposed.