What size is a 1 carat moissanite?

If the 1 ct is diamond equivalent weight, about 6.5 mm round, the size of a 1 ct diamond. If it is a real weight of 1.00 ct, the stone is a little larger. Most listings use DEW, so ask.

How much does a 6.5 mm moissanite really weigh?

About 0.93 ct by density at typical depth (range 0.88 to 1.01 ct). Many sellers publish 0.88 ct, which reflects a slightly shallower cut. Only weighing settles it.

What is the moissanite equivalent of a 2 carat diamond?

A round moissanite of about 8.1 mm, the size of a 2 ct diamond. At 8 mm, our chart gives 1.91 ct DEW and about 1.74 ct real weight.

Why does my moissanite certificate list a lower weight?

Certificates and invoices that list a real weight will usually show less than the DEW, because moissanite is lighter than diamond.

Is moissanite sold by millimetre?

Often, yes, especially loose stones. Millimetre size is the most reliable way to compare moissanite with diamond, because it removes the DEW question entirely.

Does this chart work for oval or other shapes?

The main chart is for rounds. A 1 ct real-weight oval moissanite at a 1.4 ratio is about 8.2 x 5.9 mm. Use the carat to mm calculator for any shape.

Moissanite Size Chart: mm, DEW and Real Weight

Round moissanite by millimetre

Moissanite is lighter than diamond, about 91.5% of diamond's density. So every moissanite has two weights you might see: its diamond equivalent weight (DEW), which is what a diamond of the same size would weigh, and its real weight, which is lower. This chart shows both for each millimetre size, generated by our formula engine.

Round moissanite: diameter, DEW and estimated real weight
Diameter	DEW (diamond of this size)	Real weight, estimate	Real weight range
3 mm	0.10 ct	0.090 ct	0.090 to 0.10 ct
3.5 mm	0.16 ct	0.15 ct	0.14 to 0.16 ct
4 mm	0.24 ct	0.22 ct	0.21 to 0.24 ct
4.5 mm	0.34 ct	0.31 ct	0.29 to 0.34 ct
5 mm	0.47 ct	0.43 ct	0.40 to 0.46 ct
5.5 mm	0.62 ct	0.57 ct	0.54 to 0.61 ct
6 mm	0.80 ct	0.74 ct	0.69 to 0.79 ct
6.5 mm	1.02 ct	0.93 ct	0.88 to 1.01 ct
7 mm	1.28 ct	1.17 ct	1.10 to 1.26 ct
7.5 mm	1.57 ct	1.44 ct	1.36 to 1.55 ct
8 mm	1.91 ct	1.74 ct	1.65 to 1.88 ct
8.5 mm	2.29 ct	2.09 ct	1.98 to 2.26 ct
9 mm	2.71 ct	2.48 ct	2.35 to 2.68 ct
9.5 mm	3.19 ct	2.92 ct	2.76 to 3.15 ct
10 mm	3.72 ct	3.40 ct	3.22 to 3.68 ct
11 mm	4.95 ct	4.53 ct	4.28 to 4.89 ct
12 mm	6.43 ct	5.88 ct	5.56 to 6.35 ct

The real weight is simply the DEW multiplied by 0.9148, the ratio of moissanite's density (3.22) to diamond's (3.52). Sellers sometimes publish lower real weights, such as 0.88 ct for a 6.5 mm round, which points to moissanite being cut a little shallower than the ideal diamond our formula assumes. Both figures are shown on the moissanite vs diamond size page.

Fancy shape moissanite by real weight

These tables work the other way: they start from a real moissanite weight and give the face-up size. If a listing gives DEW, use the diamond size chart for the shape instead, since DEW means "the size of a diamond of this weight".

Oval moissanite, real weight to size (ratio 1.4, depth 61%)
Real ct	0.25	0.50	0.75	1.00	1.50	2.00	3.00
Size (mm)	5.2 x 3.7	6.5 x 4.7	7.5 x 5.3	8.2 x 5.9	9.4 x 6.7	10.3 x 7.4	11.8 x 8.4

Princess (square brilliant) moissanite, real weight to size (ratio 1, depth 70%)
Real ct	0.25	0.50	0.75	1.00	1.50	2.00	3.00
Size (mm)	3.6	4.6	5.2	5.7	6.6	7.2	8.3

Cushion (square) moissanite, real weight to size (ratio 1, depth 70%)
Real ct	0.25	0.50	0.75	1.00	1.50	2.00	3.00
Size (mm)	4.0	5.0	5.7	6.3	7.2	7.9	9.0

Emerald cut (rectangular step) moissanite, real weight to size (ratio 1.4, depth 62%)
Real ct	0.25	0.50	0.75	1.00	1.50	2.00	3.00
Size (mm)	4.6 x 3.3	5.8 x 4.1	6.6 x 4.7	7.3 x 5.2	8.3 x 6.0	9.2 x 6.6	10.5 x 7.5

Rectangle with cut corners (radiant style) moissanite, real weight to size (ratio 1.25, depth 64%)
Real ct	0.25	0.50	0.75	1.00	1.50	2.00	3.00
Size (mm)	4.3 x 3.4	5.4 x 4.3	6.2 x 4.9	6.8 x 5.4	7.8 x 6.2	8.5 x 6.8	9.8 x 7.8

Pear moissanite, real weight to size (ratio 1.55, depth 61%)
Real ct	0.25	0.50	0.75	1.00	1.50	2.00	3.00
Size (mm)	5.7 x 3.6	7.1 x 4.6	8.2 x 5.3	9.0 x 5.8	10.3 x 6.6	11.3 x 7.3	12.9 x 8.3

How to use this chart when buying

Find the millimetre size. Most moissanite listings give it. It is the most reliable figure because it does not depend on which weight convention is used.
Check the weight label. "DEW", "diamond equivalent" or "ct DEW" means the size figure in disguise. A plain "ct" might mean either. Ask.
Compare like with like. Compare moissanite DEW with diamond carat weight, or moissanite real weight with other moissanite real weights. Mixing them makes moissanite look either bigger or lighter than it is.

Why moissanite is sold by DEW

Shoppers know diamond sizes by carat. A buyer looking for "a 1 carat look" wants a stone about 6.5 mm across. Selling that stone as "0.93 ct" would make it sound smaller than the diamond it is meant to match, so the market adopted DEW as a size label. It is a convention, and there is nothing wrong with it as long as listings say clearly that it is an equivalent weight.

Our DEW calculator converts any weight, and the carat to mm finder covers every shape. For small stones, a 5 mm round is about 0.47 ct DEW and 0.43 ct real.

Sources and method

Weight estimates use the colored-stone shape factors published by the International Gem Society and the Dendritics standard formula, and the diamond trade constants and length to width ratio tables published in jewelry trade references (Esslinger, Omni, Octonus). Specific gravity values are cross-checked against the International Gem Society density tables, the USGS Natural Gemstones report and GemSelect. The 0.88 ct figure for a 6.5 mm stone is a seller convention and is not independently verified.

Every number on this page is generated by the same formula engine as the calculators. Read the full method, constants and limits and the editorial policy. Data last verified 2026-11-04.

Estimates only. This is not an appraisal, grading report or valuation. A calibrated scale or a lab report is the only real weight.

Moissanite Size Chart

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