Moissanite size chart: mm to carat

By HeyGema™ · Updated November 5, 2026

In short

Moissanite is sold by its size in mm. A 6.5 mm round moissanite is labeled 1 carat, which is its diamond equivalent weight (DEW). It actually weighs about 0.91 carat, because moissanite (3.22) is lighter than diamond (3.52).

Carat to mm calculator

ShapeGemLength (mm)

About 0.94 carat

An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.

Round moissanite: mm to carat

The first column is the size you can measure. Stores label a moissanite with the weight of a diamond of that size, the second column. The third column is what the stone weighs on a scale.

4 mm: Diamond equivalent weight: 0.24 ct; True weight: 0.22 ct

5 mm: Diamond equivalent weight: 0.47 ct; True weight: 0.43 ct

5.5 mm: Diamond equivalent weight: 0.62 ct; True weight: 0.57 ct

6 mm: Diamond equivalent weight: 0.8 ct; True weight: 0.73 ct

6.5 mm: Diamond equivalent weight: 1.02 ct; True weight: 0.93 ct

7 mm: Diamond equivalent weight: 1.28 ct; True weight: 1.17 ct

7.5 mm: Diamond equivalent weight: 1.57 ct; True weight: 1.44 ct

8 mm: Diamond equivalent weight: 1.91 ct; True weight: 1.75 ct

9 mm: Diamond equivalent weight: 2.72 ct; True weight: 2.49 ct

10 mm: Diamond equivalent weight: 3.73 ct; True weight: 3.41 ct

11 mm: Diamond equivalent weight: 4.96 ct; True weight: 4.54 ct

12 mm: Diamond equivalent weight: 6.44 ct; True weight: 5.89 ct

Diameter	Diamond equivalent weight	True weight
4 mm	0.24 ct	0.22 ct
5 mm	0.47 ct	0.43 ct
5.5 mm	0.62 ct	0.57 ct
6 mm	0.8 ct	0.73 ct
6.5 mm	1.02 ct	0.93 ct
7 mm	1.28 ct	1.17 ct
7.5 mm	1.57 ct	1.44 ct
8 mm	1.91 ct	1.75 ct
9 mm	2.72 ct	2.49 ct
10 mm	3.73 ct	3.41 ct
11 mm	4.96 ct	4.54 ct
12 mm	6.44 ct	5.89 ct

Moissanite size by shape

What diamond equivalent weight means

A 1 carat diamond is 6.5 mm across. A moissanite that size weighs about 0.91 carat, but sellers call it 1 carat DEW so you can compare it with a diamond of the same look. If a listing gives only a weight and no size, ask for the size in mm.

Questions

A 6.5 mm round moissanite is sold as 1 carat DEW. It weighs about 0.91 carat.

No. Moissanite is lighter, so a 1 carat moissanite is 6.6 mm across, a little bigger than a 1 carat diamond (6.5 mm). Most stores label by DEW, so a 1 carat DEW moissanite is the same size as a 1 carat diamond.

DEW is diamond equivalent weight: the weight a diamond of the same size would have. It is how most moissanite is labeled.