Moissanite Size Chart: MM to Carat, and How Big Each Size Looks

Two-carat rainbow moissanite statement ring in sterling silver

From delicate everyday studs to a 2-carat statement — size, visualised

One of the hardest parts of buying moissanite online is judging how big a stone will actually look once it's on your hand or in your ear. A number like “1 carat” or “2 carat” doesn't mean much in the abstract, and photos can be misleading. This guide fixes that: a clear millimetre-to-carat chart, plus a plain description of how each size reads in real life, so you can choose with confidence and avoid the disappointment of a stone that arrives smaller — or larger — than you pictured.

There's one quirk to understand first, and then the chart does the rest.

Why moissanite is measured in millimetres and carats

Carat is a unit of weight, not size. Because moissanite is about 15% less dense than diamond, a moissanite and a diamond of the same physical width weigh slightly different amounts. To keep things clear, moissanite is described by its millimetre size (its actual width) and by a “carat equivalent”, sometimes written DEW (diamond equivalent weight) — meaning “the same size as a diamond of this many carats.”

The practical upshot is simple: when you want to know how big a moissanite will look, follow the millimetres. When a piece is sold as “1 carat,” it almost always means “the visual size of a 1-carat diamond,” which is exactly what you care about. (For how size interacts with colour, clarity and cut, see our companion guide to moissanite colour and clarity grades.)

Moissanite size chart (round brilliant)

MM size Approx. carat equivalent How it reads
3.0 mm ~0.10 ct Petite — second-hole studs, delicate accents
4.0 mm ~0.25 ct Subtle, understated everyday stud
5.0 mm ~0.50 ct Classic everyday stud or pendant size
6.5 mm ~1.0 ct The classic solitaire look — clearly visible, still elegant
7.5 mm ~1.5 ct Generous and eye-catching without being over the top
8.0 mm ~2.0 ct Big, confident, definitely noticed
9.0 mm ~2.75 ct Statement scale
10.0 mm ~3.5 ct Full showpiece

These figures are approximate and apply to round brilliant stones. Fancy shapes carry their size differently — more on that below.

How to choose a size for a ring

For a ring, the “right” size is a balance between the look you want and your hand. A 6.5mm (1-carat-equivalent) stone is the timeless solitaire size and flatters almost everyone. Go up to 8mm (2ct) and above for real statement presence — as with our Rainbow Moissanite Statement Ring — or down to 5mm for something dainty and everyday, like the 0.5-carat Heart Moissanite Halo Ring. Two things to keep in mind: slimmer or shorter fingers make a given stone look proportionally larger, so you may not need to size up as much as you think; and a halo setting (a ring of small stones around the centre) makes the whole ring read bigger without a bigger centre stone.

How to choose a size for stud earrings

Studs are quoted per stone, so remember you're buying a pair. For everyday studs, 4–5mm (roughly 0.25–0.5ct each) is the sweet spot — present enough to sparkle, refined enough for daily wear and work. Step up to 6–6.5mm for studs with real impact for evenings and occasions. Beyond about 7mm, studs start to feel properly bold. Earlobe size matters too: a larger stud suits a fuller lobe, while petite lobes are flattered by 4–5mm. Precision-cut geometric studs like our Square Moissanite Studs can look a touch larger than a round of the same width because of their shape.

How to choose a size for a pendant

For a pendant, scale to the chain length and neckline. A 5–6.5mm stone reads beautifully on a standard 16–18″ chain for everyday wear; a larger stone or a drop design like the Moissanite Butterfly Lariat makes more of a statement for occasions. If you're unsure how a length will sit, our necklace length guide shows where each size falls.

A quick note on shape

Two stones can share a carat-equivalent weight and still look different sizes, because shape changes how the weight is distributed. Elongated shapes — oval, marquise, emerald, pear — tend to look larger than a round of the same carat, because they cover more surface area on the finger. Round and cushion shapes look true to size. So if you want maximum visual size for your money, an elongated cut is a clever trick.

Should you size up because moissanite is affordable?

It's tempting — moissanite's low price means a 2-carat look costs a fraction of the diamond equivalent, so why not go big? The honest answer: buy the size that suits the wearer and the piece, not the biggest number you can afford. A beautifully proportioned 1-carat solitaire looks far more elegant on a slim hand than an oversized stone that overwhelms it. Presence is about proportion, not just millimetres. Because moissanite is affordable, you have the freedom to choose by taste rather than budget — use it.

The bottom line

Moissanite is sold in millimetres and “carat equivalents,” and the millimetre figure is the one that tells you how big a stone will truly look. Use the chart above as your reference: around 6.5mm for the classic 1-carat solitaire look, 4–5mm for refined everyday studs, and 8mm-plus for statement scale — adjusting for your hand, lobe or neckline, and remembering that elongated shapes and halo settings both read larger. Choose by proportion rather than by chasing the biggest number, and your moissanite will look just right.

See sizes across the range in our Moissanite Collection — every piece lists its millimetre and carat-equivalent size.

Related reading:
Moissanite Engagement Rings UK: The Complete Buyer's Guide
How to Find Your Ring Size at Home (Without Guessing)
Necklace Length Guide: How to Choose the Perfect Chain Length