What Size Moissanite Looks Like a 1-Carat Diamond? The Complete Size Guide

August 29, 2026

A 1-carat moissanite looks like a 1-carat diamond. Moissanite and diamond have nearly identical dimensions at equivalent carat weights — but because moissanite is slightly less dense than diamond, a 1-carat moissanite is actually slightly larger in diameter than a 1-carat diamond. Here is the complete size comparison.

Why Carat Weight and Physical Size Are Different Things

Carat is a unit of weight, not size. A 1-carat diamond weighs 0.2 grams. A 1-carat moissanite also weighs 0.2 grams — but because moissanite is less dense than diamond (3.21 g/cm³ vs. diamond's 3.52 g/cm³), a 1-carat moissanite is physically slightly larger than a 1-carat diamond.

In practice, this means that when moissanite is sold by carat weight equivalent to diamond, the actual stone is marginally larger. This is a benefit, not a drawback — you get slightly more visual size for the same stated carat weight.

Moissanite vs. Diamond: Size Comparison by Carat

0.5 carat diamond equivalent: ~5.0mm diameter (round brilliant)
Moissanite at same weight: ~5.1mm diameter

1 carat diamond equivalent: ~6.5mm diameter (round brilliant)
Moissanite at same weight: ~6.5–6.6mm diameter

1.5 carat diamond equivalent: ~7.4mm diameter (round brilliant)
Moissanite at same weight: ~7.5mm diameter

2 carat diamond equivalent: ~8.1mm diameter (round brilliant)
Moissanite at same weight: ~8.1–8.2mm diameter

3 carat diamond equivalent: ~9.4mm diameter (round brilliant)
Moissanite at same weight: ~9.4–9.5mm diameter

The differences are small — fractions of a millimeter — and not visible to the naked eye. For all practical purposes, a 1-carat moissanite looks the same size as a 1-carat diamond on the finger.

How Moissanite Is Sold: By Diamond Equivalent Weight (DEW)

Most moissanite sellers, including Moissanite Shine, sell moissanite by Diamond Equivalent Weight (DEW) — the carat weight of a diamond that would be the same physical size as the moissanite. This makes it easy to compare sizes across different stone types.

When you see a "1 carat moissanite," it means a moissanite that is the same physical size as a 1-carat diamond — approximately 6.5mm in diameter for a round brilliant cut.

Which Size Is Right for You?

The most popular sizes for engagement rings are 1–2 carats. A 1-carat round brilliant moissanite (6.5mm) is a classic, elegant size that looks substantial on most hand sizes without being overwhelming. A 2-carat (8.1mm) makes a bold, glamorous statement. A 1.5-carat (7.4mm) is a beautiful middle ground.

For guidance on choosing the right size for your partner's hand, see: Choosing the Perfect Carat Weight.

Ready to choose your size? Browse our engagement ring collection — all DEF color, VVS1 clarity, GRA-certified. Or explore our best-selling jewelry.

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