Why Moissanite Weighs Less Than Diamond: Specific Gravity in Plain English

You've probably seen "1 carat DEW" on moissanite listings and wondered what it means. Or noticed that moissanite seems to look slightly larger than a diamond of the same carat weight. The answer to both questions is the same: moissanite weighs less than diamond. Not because it's lower quality — but because of physics. Here's the plain-English explanation.

The Simple Version First

Imagine two balls, both exactly the same size — one made of wood, one made of iron. They look identical. But the iron ball is much heavier. Now imagine those two balls are gemstones: moissanite (the wood) and diamond (the iron). Same physical size. Different weight.

This is what gemologists call specific gravity: how dense a material is. Moissanite's specific gravity is 3.21. Diamond's is 3.52. Diamond is about 10% denser than moissanite for the same volume. That's the whole thing — everything else is detail.

What This Means When You're Shopping

In jewelry, "carat" measures weight, not size. One carat equals 0.2 grams. So when you compare a 1-carat diamond and a 1-carat moissanite, you're comparing two stones of the same mass. But because moissanite is lighter per unit of volume, a 1-carat moissanite is physically slightly larger than a 1-carat diamond.

A 1-carat round diamond measures approximately 6.5mm across. A 1-carat round moissanite measures approximately 6.7mm — visibly larger face-up, because the same weight of moissanite takes up more physical space than the same weight of diamond. You get more visible stone per carat.

What Does "DEW" Mean on Moissanite Listings?

Because of this density difference, moissanite is commonly sold using Diamond Equivalent Weight (DEW). Instead of listing the stone's true carat weight, DEW tells you what physical size of diamond the moissanite matches visually.

"1.00 ct DEW moissanite" means: this stone looks the same size as a 1-carat diamond. Its true weight is about 0.88 carats — but it appears identical in size to a 1-carat diamond on your finger.

For a full visual reference, see our carat size guide and DEW vs. carat guide.

Does Moissanite Feel Lighter on Your Hand?

Technically yes — but the difference is imperceptible. A 1 ct DEW moissanite stone weighs about 0.176 grams; the equivalent diamond weighs 0.2 grams. Less than a quarter of a gram difference. You will never notice it in daily wear.

The comparison that is noticeable is moissanite vs. cubic zirconia. CZ has a specific gravity of 5.60–6.00 — nearly double moissanite's. A CZ ring of the same apparent size is genuinely heavier on your hand. Buyers who switch from CZ to moissanite often notice the difference immediately. See our moissanite vs. CZ guide.

Does Lower Density Mean Lower Quality?

Not at all. Specific gravity is a fixed property of a material's chemical composition — it has nothing to do with cut quality, clarity, or brilliance. A DEF/VVS1 moissanite with SG 3.21 is every bit as beautiful as a diamond with SG 3.52. They're different materials with different atomic structures, each with exceptional properties of their own. See our grading guide to understand what actually determines quality, and our advanced specific gravity guide for the complete gemology science.

The One-Sentence Summary

Moissanite weighs less than diamond for the same visible size — which is why a 1 ct DEW moissanite looks identical to a 1-carat diamond, costs a fraction of the price, and gives you slightly more stone per carat than diamond does.

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