Moissanite vs Natural Diamond Size Chart

Discover the key differences between moissanite and natural diamonds,
from sparkle and durability to value and appearance.

Natural Diamond

Moissanite

Same size on the finger, different number on the label.

Diamonds are priced and described by carat weight. Moissanite is described by millimetre dimensions because it is slightly less dense than diamond, so a moissanite that is exactly the same size as a 1 carat diamond actually weighs slightly less than 1 carat.

To keep things simple, moissanite is matched to diamonds using DEW (Diamond Equivalent Weight). A stone sold as 1 ct DEW is cut to the same millimetre size as a 1 ct diamond (about 6.5 mm for a round), so it looks identical on the hand even though its actual weight is closer to 0.9 ct. This page provides the complete mm to carat size chart for every popular diamond shape.

Why moissanite is measured in millimetres, not carats

It comes down to density. A carat is a unit of weight (1 ct = 0.20 g), but what your eye actually sees is the stone's face up size in millimetres. Moissanite is slightly less dense than diamond, so two stones of the same size do not weigh the same.

Moissanite

Lighter for its size

Moissanite has a specific gravity of about 3.21. Because it is less dense, describing it by carat weight would be misleading. The same weight would appear larger than a diamond. Instead, moissanite is sold by its face up size in millimetres.

Specific gravity ≈ 3.21
Sold by Millimetre size
Matched to diamonds via DEW
Natural Diamond

Heavier for its size

Natural diamond has a specific gravity of about 3.52, roughly 10% denser than moissanite. A diamond and a moissanite cut to the same millimetre dimensions will therefore have different carat weights by about that amount.

Specific gravity ≈ 3.52
Sold by Carat weight
1.00 ct round diameter ≈ 6.5 mm

Lab-Grown Vs Natural: The Complete Comparison

Everything that matters when choosing a diamond, including quality, beauty, price, ethics and value, in one honest comparison.

MM Size Diamond Carat Moissanite DEW Moissanite Actual Weight
3.0 mm 0.10 ct 0.10 ct ≈ 0.09 ct
3.5 mm 0.15 ct 0.15 ct ≈ 0.13 ct
4.0 mm 0.25 ct 0.25 ct ≈ 0.22 ct
4.5 mm 0.35 ct 0.35 ct ≈ 0.31 ct
5.0 mm 0.50 ct 0.50 ct ≈ 0.44 ct
5.5 mm 0.67 ct 0.67 ct ≈ 0.59 ct
6.0 mm 0.80 ct 0.80 ct ≈ 0.70 ct
6.5 mm 1.00 ct 1.00 ct ≈ 0.88 ct
7.0 mm 1.25 ct 1.25 ct ≈ 1.10 ct
7.5 mm 1.50 ct 1.50 ct ≈ 1.32 ct
8.0 mm 2.00 ct 2.00 ct ≈ 1.76 ct
8.5 mm 2.50 ct 2.50 ct ≈ 2.20 ct
9.0 mm 3.00 ct 3.00 ct ≈ 2.64 ct
9.5 mm 3.50 ct 3.50 ct ≈ 3.08 ct
10.0 mm 4.00 ct 4.00 ct ≈ 3.52 ct
10.5 mm 4.50 ct 4.50 ct ≈ 3.96 ct
11.0 mm 5.00 ct 5.00 ct ≈ 4.40 ct
11.5 mm 5.80 ct 5.80 ct ≈ 5.10 ct
12.0 mm 6.50 ct 6.50 ct ≈ 5.72 ct
12.5 mm 7.20 ct 7.20 ct ≈ 6.34 ct

Notice the DEW column and the Diamond Carat column are identical. That is the whole purpose of Diamond Equivalent Weight (DEW). The final column shows why: a moissanite of the same size typically weighs 10–12% less because it is less dense than a diamond. Values are approximate. Always confirm the stone's measured dimensions before purchasing.

Frequently Asked Questions

Why is moissanite measured in millimetres instead of carats?

Moissanite is measured in millimetres (mm) because carat measures weight, not size. Since moissanite is less dense than diamond, two stones with the same face up size will have different carat weights. Measuring in millimetres gives a more accurate comparison of how large the stone will appear when worn.

What does Diamond Equivalent Weight (DEW) mean?

Diamond Equivalent Weight (DEW) is a reference used to compare the visible size of a moissanite with a diamond. For example, a 1 ct DEW moissanite has the same face up dimensions as a 1 carat diamond, even though its actual weight is lower because moissanite is less dense.

Is a 1 carat moissanite the same size as a 1 carat diamond?

Not exactly. A moissanite that actually weighs 1 carat will appear slightly larger than a 1 carat diamond because it is less dense. To avoid confusion, most jewellers sell moissanite using millimetre measurements or Diamond Equivalent Weight (DEW) rather than actual carat weight.

How do I choose the right moissanite size?

Start with the millimetre dimensions, not the carat label. If you know the diamond size you want, use a Moissanite vs Diamond Size Chart to find the matching mm size or DEW. This ensures your moissanite has the same visual appearance as the equivalent diamond.

Does moissanite look bigger than a diamond?

Only if you compare actual carat weight. When both stones have the same millimetre dimensions, they appear virtually the same size on the finger. The difference is in weight, not visible size, which is why millimetres and DEW are the preferred way to compare moissanite with diamonds.

Contact Us

Still unsure about moissanite or natural diamonds?

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