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Moissanite's carat figure is a size label borrowed from diamond, not a weight of moissanite. A round stone marketed as 1 carat, 2 carat or 3 carat is cut to roughly the same millimetre diameter as a diamond of that carat weight — about 6.5 mm, 8 mm and 9.3–9.6 mm across — so it reads as the same size face-up. The moissanite itself weighs less than that number implies, because silicon carbide is a lighter material than diamond for the same volume.
What does a moissanite "carat" actually mean?
Diamond carat is a unit of mass, plainly: one carat is 0.2 grams, no more and no less. Moissanite is not weighed the same way when it goes on a listing. Because buyers shop for moissanite already fluent in diamond carats, most sellers — us included — quote a size figure the trade calls diamond equivalent weight, or DEW. DEW is the carat weight a diamond would be if it were cut to the same millimetre diameter as the moissanite in front of you.
That is a size comparison, not a weight. It gets used interchangeably with real carat weight in casual conversation, and that is where the confusion starts. Two stones can share a carat label and differ in actual mass, and moissanite is exactly that case.
Why doesn't a moissanite weigh what its carat figure says?
The gap comes down to density. Diamond has a specific gravity of about 3.52. Moissanite, which is silicon carbide rather than carbon, sits at about 3.22. Moissanite is about 8.5% less dense than diamond, so a stone matched to a diamond's size weighs less than that diamond does. Cut two stones to the identical millimetre diameter and the diamond is always the heavier of the pair, because more mass is packed into the same space.
In practice, a round moissanite cut to the roughly 6.5 mm diameter of a 1-carat diamond weighs in at somewhere around 0.88 to 0.91 actual carats, even though it is listed and sold as a 1-carat stone by size. That gap comes from density rather than size, so it holds at roughly the same proportion at a 2-carat or 3-carat look too.
What size actually maps to 1ct, 2ct and 3ct?
For a round brilliant cut, reference sizes are widely published and reasonably consistent across labs and retailers, though the exact figure moves a little with how deep or shallow the stone is cut.
| DEW (round cut) | Approx. diameter | How it reads worn |
|---|---|---|
| 1.00 ct | ~6.5 mm | A quiet single point of light — a modest stud or pendant |
| 2.00 ct | ~8 mm | Noticeable across a table, the size most people picture as "a real stone" |
| 3.00 ct | ~9.3–9.6 mm | A statement piece, visible from across a room |
Those millimetre figures assume a well-proportioned round brilliant. A stone cut too deep hides weight below the surface and looks smaller than its DEW number promises; cut too shallow, it can look larger at some cost to brilliance. This is why we list our own stones by millimetre width rather than carat — millimetres are the figure a shallow or deep cut cannot quietly distort.
What a 1-carat moissanite actually looks like worn
At roughly 6.5 mm, a 1-carat-look stone is present without being loud. In our own moissanite stud earrings, the 6 mm and 6.5 mm widths sit right at that mark, and they are the sizes most people buying their first pair land on: visible without taking over the ear. In the floating solitaire necklace, the 6.5 mm option is the smallest of the three we offer, and the product page itself calls it a quiet everyday size. That is what a 1-carat DEW stone does at the throat — a single clean point of light rather than a centrepiece.
What a 2-carat moissanite actually looks like worn
At around 8 mm, a stone crosses from noticeable to hard to miss. Both pieces above top out close to this size: the stud earrings go up to 8 mm, and the largest stone in the floating solitaire is also 8 mm. We describe that top size on both listings as the one people notice — earrings that read as jewellery from across a room, a solitaire that becomes the only piece a neckline needs.
What a 3-carat moissanite actually looks like worn
Here is the honest gap in our own range: none of our single-stone earrings or solitaire pendants reach 9.3 to 9.6 mm. The largest single stones we carry, at 8 mm, sit at the 2-carat mark, not the 3-carat one. For a sense of what a stone that much larger does on skin, the closer reference in our catalogue is the eternity band, where individual stones run from 1.7 mm up to 4 mm each around a continuous line — many smaller stones rather than one large one, but the photograph below still shows how a few millimetres change what a stone does.
A single round stone at the 3-carat DEW mark is a real, buyable size in the wider moissanite market — we simply do not stock a single-stone earring or pendant that large right now. If that is what you are after, say so through our contact page and we will tell you honestly whether it is something we can source.
Does the diamond-equivalent number matter when you are buying?
Less than it seems to. Because DEW is a size comparison rather than a weight, two stones both labelled 1 carat from two different sellers should look the same size if both are genuinely cut to about 6.5 mm. What actually varies between sellers is cut quality, clarity grade and how the stone is set, none of which the carat number tells you.
We have covered the wider comparison between moissanite, lab diamond and mined diamond — price tier, hardness and how each is graded — in a separate cost and property breakdown. If you are weighing moissanite specifically for an engagement ring, we have also written honestly about who it suits and where it falls short.
Sizes we carry
Moissanite stud earringsfive widths, 3mm to 8mm, roughly a 1 to 2-carat look
Floating solitaire necklace6.5mm, 7mm and 8mm, in rhodium or gold tone
Moissanite eternity bandcontinuous stones, 1.7mm to 4mm each, pictured above
Marquise-cut moissanite ringa single 1-carat DEW stone in an elongated cut
Moissanite tennis braceleta continuous line of prong-set stones, three widths
Moissanite cross pendantstones set across the arms, one size
Browse the full range by category — rings, earrings, bracelets and necklaces — or start with our best sellers, which is where most people begin.
Common questions
Is a 1-carat moissanite the same size as a 1-carat diamond?
Yes, in millimetres. A round moissanite marketed as 1 carat is cut to about the same 6.5mm diameter as a 1-carat diamond, so it reads the same size face-up. The moissanite itself weighs somewhat less than 1 carat, because it is a less dense material.
Why is moissanite sold in millimetres instead of carats?
Because millimetre width is the stone's true, unambiguous size, while the carat figure quoted for moissanite is a comparison to a diamond of that carat weight rather than the stone's own weight. We list our stone sizes in millimetres for that reason.
Does a 2-carat moissanite weigh 2 carats?
No. Because moissanite is about 8.5% less dense than diamond, a stone cut to the same face-up size as a 2-carat diamond weighs somewhat less than 2 carats — the same proportional gap that shows up at 1 carat and 3 carats.
What is the largest single moissanite stone Aqua Gold carries in a stud earring or pendant?
8mm, which corresponds to roughly a 2-carat diamond-equivalent size. We do not currently carry a single stone at the 3-carat, 9.3–9.6mm mark in our stud earrings or solitaire necklace.
Does a bigger carat figure mean a more valuable stone?
It means a larger, more noticeable stone, and larger moissanite generally costs more within its own range. It does not carry the same rarity signal a large mined diamond does, because moissanite is grown to order rather than found in limited supply.
Which size should you start with?
If you have not worn moissanite before, the 3 mm or 4 mm stud earrings are a low-commitment way to see the stone in daylight before choosing anything larger. For a first piece at the 1-carat mark, the 6.5 mm option in either the stud earrings or the floating solitaire is the size most people settle on. If you already want the 2-carat look, the 8 mm stone is available in both.
More questions
We answer shipping, returns, sizing and payment questions on our FAQ page. If something is not covered there, get in touch and a person from the workshop will answer.
References
The specific gravity figures in this article — about 3.52 for diamond and about 3.22 for moissanite — are drawn from published gemological measurements rather than marketing copy, and are consistent with the technical properties Charles & Colvard, the original commercial producer of moissanite, publishes for its material. Millimetre-to-carat figures for round brilliant cuts are standard industry reference values and shift slightly with cut proportions; where sources disagreed by a fraction of a millimetre, we have given a range rather than a single false-precise number.
