The trillion is one of the sharpest, most graphic shapes in jewellery — a triangle with three equal sides, cut flat and wide, throwing light in broad slabs rather than pinpoint glitter. People either walk past it entirely or stop dead and want nothing else.

If you are in the second group, the practical question follows quickly: does something that distinctive cost more than a conventional diamond?

What a trillion cut is

A trillion — also written trilliant or trillian, depending on who cut it — is a triangular diamond, usually with 31 to 50 facets. The sides can be straight, giving a crisp geometric outline, or gently curved, which softens the look and is sometimes called a trilliant.

Two features define it. First, it is shallow: trillions are cut wide and flat rather than deep. Second, its facets are large and broad, so instead of the rapid coloured fire of a round brilliant you get wide, bold flashes.

The shape has two lives. As a centre stone it is bold, architectural and unmistakably deliberate. As a side stone it is one of the classic partners for a bigger central diamond, its straight edge sitting flush against the centre and its point running down the shoulder of the ring.

Are trillion cut diamonds more expensive?

Per carat, no. Trillions are generally less expensive than round brilliants of the same weight and grades, and often less than most other shapes too.

The reasons are the familiar ones.

They use the rough well. A shallow triangle can be cut from crystal shapes that would make a poor round. Trade wisdom has long put the loss from cutting a round brilliant at around half the rough weight; a trillion keeps considerably more. Less waste means a lower price per finished carat.

Demand is modest. Round brilliants are the most requested shape in the world and that popularity holds their price up. Trillions are a specialist taste, and specialist tastes are usually cheaper.

They look bigger than they weigh. Because a trillion is shallow, its weight sits across the top where you can see it rather than underneath the setting where you cannot. A trillion presents a notably larger face-up size than a round of the same carat weight. Per visible millimetre, it is one of the better-value shapes available.

	Trillion	Round brilliant
Outline	Triangle, straight or curved sides	Circle
Facets	Roughly 31 to 50	57 or 58
Depth	Shallow	Deep
Size for the weight	Looks larger	Carries hidden weight below
Sparkle character	Broad bold flashes	Rapid coloured fire
Price per carat	Lower	Highest of the common shapes
Official cut grade on the report	No	Yes

Where trillions do cost you more

The headline per-carat saving is real, but three things claw some of it back. Being honest about them is the whole point of this article.

1. Clarity has to be higher

A shallow stone with large open facets is a stone you can see into. An inclusion — one of the small natural marks that form inside every diamond as it grows — has nowhere to hide.

On the clarity scale, which runs FL (flawless) at the top, then IF, VVS1, VVS2, VS1, VS2, SI1, SI2 and down to I3, many buyers happily use SI1 in a round brilliant and never see a thing. In a trillion, an SI1 inclusion may be plainly visible. Budget for VS2 or better.

The same applies to colour on the D-to-Z scale. Fewer, broader facets means less bouncing light to disguise a warm tint, so a trillion shows its body colour more honestly than a brilliant cut does.

2. The points need protecting

Diamond is the hardest natural material, but hardness and toughness are different things. A sharp corner concentrates any impact, and a trillion has three of them.

Good trillion settings use V-shaped claws that wrap each point, or a bezel — a continuous rim of metal enclosing the stone. Both take more bench time than the simple claws on a round. On a hand-made ring that is a genuine, if modest, extra cost, and it is not optional.

3. Matching pairs cost a premium

Trillions are most often bought in pairs, flanking a centre stone. Two trillions that match in size, outline, colour and clarity are considerably harder to find than one, and matched pairs are priced accordingly. If you want a three-stone ring with trillion sides, expect the pair to cost more than double a single stone.

Trillions in three-stone designs

The classic use is a three-stone ring: a large centre with a trillion on each shoulder. The straight edge of the trillion sits neatly against the centre stone, and the tapering point draws the eye along the finger, which flatters the hand.

We do not currently stock trillion cut diamonds, but the three-stone architecture is one of our favourite forms and you can see how it works in our Three Stone Emerald Cut Engagement Ring and our Three Stone Cushion Cut Engagement Ring. If you want a trillion version, we make bespoke pieces at no extra design cost — we will source the stones, match the pair, and hand-make the ring in solid gold or platinum in our North Harrow workshop, with a free IGI certificate on the centre stone.

If it is the geometric character you are drawn to rather than the triangle specifically, our stocked angular shapes get you close. A design like the Solitaire Hexagon Cut Engagement Ring has the same clean-edged, architectural feel without the fragile points.

Buying a trillion sensibly

Five things to check, in order:

1. Symmetry. All three sides should be equal and all three points identical. Asymmetry in a triangle is far more obvious than in a round, and it is the first thing a trained eye spots.
2. Clarity to eye-clean. Look at the actual stone or a good photograph, not just the grade on the report. VS2 or better is the sensible starting point.
3. Depth. A trillion cut too shallow chasing face-up size will look watery and lifeless. There is a point where thin stops being clever.
4. Point protection. Insist on V-claws or a bezel. This is where a trillion ring succeeds or fails over ten years of wear.
5. Certificate. There is no overall cut grade for fancy shapes, so read the polish and symmetry grades and use your own eyes for the rest.

Does lab-grown change the picture?

It changes the arithmetic in the trillion’s favour. The obstacle to a good trillion has always been that it needs a cleaner stone than a brilliant does, and clean rough is expensive. When the rough costs a fraction as much, buying VS clarity instead of SI stops being a difficult decision.

Matched pairs also become far more achievable, because the searching is the cost rather than the material. Lab-grown diamonds are chemically identical to mined ones and graded on the same scales by the same laboratories. Prices have fallen a long way and are still moving, so treat any figure you read anywhere as a snapshot.

Frequently asked questions

Are trillion cut diamonds cheaper than round?

Per carat, generally yes, and they look larger for their weight. The saving narrows once you account for the higher clarity grade and the more involved setting.

Do trillion diamonds chip easily?

The three points are the vulnerable part, as with any pointed shape. A setting that covers each point with a V-claw or a bezel solves this, and well-set trillions wear perfectly well.

Can a trillion be an engagement ring centre stone?

Absolutely, and it makes a striking one. It is a bolder, more modern statement than a round, and it looks larger for the money. Just choose the setting carefully.

What clarity should I buy for a trillion?

VS2 or better as a starting point. The broad open facets show inclusions far more readily than the busy faceting of a round brilliant.

Do you sell trillion cut rings?

Not from stock at present. We make them bespoke at no extra design cost, including matched side-stone pairs, with free insured UK delivery and 30 days to return.

Browse our engagement ring collection to see the shapes we hold, or the pear cut pieces if it is the tapered, pointed silhouette that appeals to you.

More guides on this topic

• What Are the Types of Diamond Cuts? A Plain-English Guide