Moissanite and diamond have different densities, so a moissanite and a diamond of the same carat weight don't measure quite the same in millimetres. A 1ct moissanite by weight is fractionally larger in diameter than a 1ct diamond by weight, which is why we, like most moissanite sellers, quote sizes in diamond equivalent weight (DEW) rather than raw carat.
Why the same weight isn't the same size
Carat is a unit of weight, not size, one carat equals 0.2 grams, and two gemstones of different density will be different physical sizes at the same weight. Moissanite has a density of roughly 3.21 g/cm3 against diamond's roughly 3.52 g/cm3. In practice, a 1ct moissanite by weight measures about 6.6mm across, while a 1ct diamond by weight measures about 6.4 to 6.5mm. The moissanite is very slightly larger.
What diamond equivalent weight (DEW) means
DEW is the carat weight of a diamond with the same diameter as a given moissanite. Because moissanite is less dense, a moissanite that looks the same size as a 1ct diamond actually weighs slightly less than 1ct. DEW lets you compare moissanite size using the diamond carat reference you already know, rather than learning a separate measurement system. When we quote a stone as 1ct DEW or 2ct DEW, that's the visual size equivalent, not the actual weight, the true weight will be a touch lower than the DEW figure. Because DEW is standardised across the industry, a 1ct DEW moissanite from any reputable supplier measures roughly 6.5mm, which makes comparing across sellers straightforward.
Size comparison, side by side
At 0.5ct, a diamond measures roughly 5.1mm and a 0.5ct DEW moissanite roughly 5.2mm, barely perceptible. At 1ct, diamond runs about 6.4-6.5mm against moissanite's 6.5mm, visually equivalent and the standard comparison point most buyers use. At 1.5ct, diamond is about 7.3-7.4mm against moissanite's 7.4mm, a clear, substantial size. At 2ct, diamond runs about 8.0-8.1mm against moissanite's 8.1mm, large and visually impactful in any setting. At 3ct, diamond is about 9.3-9.4mm against moissanite's 9.4mm, a genuine statement stone. For oval, cushion, and other fancy shapes, sizes are expressed as length by width rather than a single diameter, but the same DEW principle applies.
What this means when you're choosing a size
You can specify your preferred stone size with us in millimetres, by DEW carat equivalent, or just by describing the look you want, we'll confirm the physical dimensions of any stone before it goes into your ring. The practical takeaway: a 1ct DEW moissanite looks the same size as a 1ct diamond on the hand. If you want a ring that reads like a 1ct diamond ring, ask for 1ct DEW. If you want to go bigger, a 2ct DEW moissanite looks like a 2ct diamond ring at a fraction of the price, our full 4Cs for moissanite guide covers cut, colour, and clarity alongside sizing.
Frequently asked questions
Is moissanite the same size as diamond?
Not exactly, moissanite is slightly less dense, so the same carat weight measures marginally larger. Industry convention uses DEW to make the comparison simple.
What is diamond equivalent weight (DEW)?
The carat weight of a diamond with the same diameter as a given moissanite. A 1ct DEW moissanite looks the same size as a 1ct diamond, even though its actual weight is slightly under 1ct.
Is a 1ct moissanite bigger or smaller than a 1ct diamond?
By actual weight, a 1ct moissanite is very slightly larger in diameter than a 1ct diamond, because moissanite is less dense.
How do I know what size moissanite to choose?
DEW carat equivalent is the most intuitive reference. Want a ring that looks like a 1ct diamond ring, choose 1ct DEW. Want maximum visual presence, go to 2ct or 3ct DEW.
Do you quote sizes in DEW?
Yes. We quote stone sizes in DEW carat equivalent and millimetre dimensions, and confirm the physical size of any stone at the quote stage.
Browse the full moissanite engagement ring collection from R13,995, or start a free design consultation and tell us the size you're picturing, we'll confirm the exact dimensions before anything is made.