Customers walk in asking for a "1-carat moissanite" and you have to explain that moissanite is sold by the millimetre. It is a small conversation, but it is the one that makes the difference between a confused customer and an informed buyer. A retailer who can convert millimetres to carat-equivalents on the spot looks expert, and the customer trusts the purchase more.

This guide gives you the conversion table and the language to use. See our loose stones range, sold by the millimetre.

Why moissanite uses millimetres

Moissanite is denser than diamond, so a 1-carat moissanite weighs more than a 1-carat diamond but looks smaller. Selling by carat would mislead the customer about the visual size. Instead, moissanite is sold by its physical diameter in millimetres, which is what the eye actually sees. A 6.5mm round is roughly a 1-carat equivalent in visual size, regardless of the carat weight on the scales.

The round conversion table

  • 5.0mm — about 0.5 carat equivalent.
  • 6.5mm — about 1 carat equivalent.
  • 8.0mm — about 1.5 carat equivalent.
  • 9.0mm — about 2 carat equivalent.
  • 10mm — about 3 carat equivalent.

These are visual equivalents, not weight equivalents. Use them to help the customer picture the stone on her finger.

Oval, pear and cushion conversions

Fancy shapes read larger per millimetre because of their outline. A 7x5mm oval looks like a 1-carat-plus stone on the hand. An 8x6mm pear reads even larger. Cushion is closer to round in visual size. When a customer wants a big look on a budget, an oval or pear in the same mm range gives more face-up size than a round. Our radiant and round stones are listed with their exact mm measurements.

The script to use with customers

When a customer asks for a "1 carat", say: "Our moissanite is sold by the millimetre, because that is what you actually see on the hand. A 6.5mm round looks about the size of a 1-carat diamond. Would you like to see that size, or go a little larger?" That reframes the conversation around visual size, which is what the customer cares about anyway. It also positions you as expert.

Why this matters for pricing

Pricing by the millimetre makes the value obvious. A 6.5mm stone and an 8mm stone have a clear, honest size difference, and the price difference reflects it. Customers who understand mm sizing compare size fairly, rather than arguing about carat weights that mean different things for different stones. This is one reason moissanite sells so well once the sizing language is clear.

The bottom line

Moissanite is sold by the millimetre, and a 6.5mm round is roughly a 1-carat visual equivalent. Learn the conversion table, use it with customers, and the sizing conversation becomes a trust-builder rather than a confusion. When you are ready to stock loose stones in the sizes customers ask for, browse the loose stones range or request a quote.

Using the size guide on the sales floor

Keep a printed mm-to-carat cheat sheet behind the counter. When a customer asks for "a one-carat", you point to the 6.5mm stone, show it on a hand, and let her decide whether to go larger. This turns a confusing conversation into a confident one, and it often leads to an upsell — once a customer sees how a 6.5mm looks, many step up to an 8mm for a more dramatic ring. The size guide is not just knowledge; it is a sales tool. The stones in our loose stones range are listed by exact mm so you can show the real thing.

Frequently asked questions

Why not sell moissanite by carat? Because moissanite is denser, so carat weight misleads about the visual size. Millimetres are honest.

What is a 1-carat equivalent in mm? Roughly 6.5mm round.

Which shape looks biggest per mm? Oval and pear, because their outline spreads across the finger.

Why millimetres beat carat weight for moissanite

Moissanite is denser than diamond, so a one-carat moissanite measures smaller than a one-carat diamond. This is why selling moissanite by carat weight misleads customers about the visual size they will actually see. Millimetres are honest: a 6.5mm round is roughly the look of a one-carat diamond, an 8mm is closer to two carats, and the customer can see the exact size on her hand. When you quote by millimetre rather than carat, there are no surprises and no returns for "it looked smaller than I expected".

Keep a printed mm-to-carat cheat sheet behind the counter. When a customer asks for "a one-carat", point to the 6.5mm stone, show it on a hand, and let her decide whether to go larger. This turns a confusing conversation into a confident one, and it often leads to an upsell — once a customer sees how 6.5mm looks, many step up to 8mm for a more dramatic ring. Oval and pear look biggest per millimetre because their outline spreads across the finger. The stones in our loose stones range are listed by exact millimetre so you can show the real thing.

Matching stone size to finger width

Millimetre size is not the whole story — it has to suit the customer's finger. A 7mm stone that looks elegant on a slim size 5 finger can look small on a broad size 8, and an 8mm stone can overwhelm a petite hand. This is why showing the stone on the customer's own hand, in a plain setting, is essential before she commits. A customer who sees the scale in person never complains that the ring "looked bigger online".

Cut quality also changes how a stone reads at a given millimetre. Two 6.5mm rounds can look different if one is cut for brighter fire and the other for deeper colour. When you hand-pick your stock, you control that difference, and you can honestly tell a customer which stone looks brightest on her hand. Oval and pear shapes spread across the finger and look largest per millimetre, which is why they are popular for customers who want presence without a huge carat. The stones in our loose stones range are listed by exact millimetre so you can match size to hand and to budget.