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Moissanite “ct” Explained: Carat vs Diamond-Equivalent

What does ct mean for moissanite?

For moissanite, “ct” most often refers to the stone’s size in carats (carat weight). Carats were originally created to describe the weight of diamonds and other gemstones. With moissanite, though, “ct” can be used in two different ways depending on the seller: actual carat weight (the stone’s weight) or “diamond equivalent” sizing (how large it looks compared to a diamond carat).

Carat weight vs. diamond-equivalent (DEW) for moissanite

Moissanite has a different density than diamond, so a moissanite and a diamond with the same dimensions won’t necessarily weigh the same. That’s why many moissanite listings use a “diamond equivalent weight” (sometimes written as “ctw DEW” or “diamond equivalent”) to communicate the face-up size most shoppers care about. In plain terms: DEW is about how big it appears; carat weight is about what it physically weighs.

What “0.3ct” usually means when shopping for moissanite

If you see something like “0.3ct” on a moissanite ring listing, it commonly indicates a diamond-equivalent look—roughly the same visible size as a 0.30 carat diamond—rather than the moissanite’s literal weight. The best way to confirm is to check whether the product page specifies millimeter measurements (for example, a square stone might be listed by its width and length) or explicitly states “diamond equivalent.” Millimeters are the most reliable way to compare shapes and sizes across diamond and moissanite.

Why “ct” still matters even if it’s not a diamond

Carat-related sizing helps set expectations for presence on the hand, design proportions, and how the center stone balances with the band and setting. It’s also useful for comparing similar styles across different metals and settings. For a concrete example of how a smaller center stone can still look substantial in a refined setting, see this guide: 18K rose gold square moissanite ring (0.3ct look).

FAQ

What does “mm” mean in moissanite sizing?

“mm” refers to the stone’s exact measurements (length and width), which is the most consistent way to judge how large a moissanite will look on the hand across different gemstones and densities.