Carats are a weight, not a size, and two stones of the same weight can look quite different. What you see on a hand is the stone's face-up size in millimetres. This guide converts between the two for all ten cuts, using our own catalogue, so every row is a stone you can order.
Why moissanite uses DEW
Moissanite is lighter than diamond: its specific gravity is 3.21 against diamond's 3.52, so a moissanite weighs roughly 10% less than a diamond of exactly the same size. Quoting its true weight would make a stone look smaller on paper than it is on the hand. So moissanite is sold by DEW, the weight a diamond of those dimensions would have. That keeps sizes comparable: a 6.5 mm round is about 1 ct whether it's diamond or moissanite. Our grading guide covers DEW with the other grades.
Different makers sometimes quote slightly different DEW for the same millimetre size. When a stone is in front of you, the millimetres are the number to trust.
How each cut changes the size you see
- Elongated cuts (oval, pear, marquise) spread their weight along the finger, so they look larger than a round of the same carat weight. A 0.91 ct oval measures 7×5mm.
- Square cuts (princess, asscher) carry more weight in their corners and depth, so they look a little smaller face-up than a round of the same weight.
- Step cuts (emerald, asscher) are cut with broad, flat facets and look larger and glassier; brilliant cuts look brighter for their size.
The best way to judge is to see it. Every stone on our stones page is shown at true size on a hand: calibrate your screen once and the size on the screen is the size on the finger.
Round moissanite size chart
| Size | Carat (DEW) |
|---|---|
| 5mm | 0.50 ct |
| 5.5mm | 0.60 ct |
| 6mm | 0.80 ct |
| 6.5mm | 1.00 ct |
| 7mm | 1.20 ct |
| 7.5mm | 1.50 ct |
| 8mm | 2.00 ct |
| 8.5mm | 2.50 ct |
| 9mm | 3.00 ct |
| 9.5mm | 3.50 ct |
| 10mm | 4.00 ct |
| 10.5mm | 4.50 ct |
| 11mm | 5.00 ct |
| 11.5mm | 5.45 ct |
| 12mm | 6.00 ct |
| 12.5mm | 7.00 ct |
| 13mm | 8.00 ct |
| 14mm | 9.00 ct |
| 15mm | 10.00 ct |
| 18mm | 15.00 ct |
| 20mm | 18.00 ct |
Cushion moissanite size chart
| Size | Carat (DEW) |
|---|---|
| 5mm | 0.65 ct |
| 5.5mm | 0.85 ct |
| 6mm | 1.13 ct |
| 6.5mm | 1.46 ct |
| 7mm | 1.66 ct |
| 7.5mm | 2.04 ct |
| 8mm | 2.63 ct |
| 8.5mm | 2.69 ct |
| 9mm | 3.17 ct |
| 9.5mm | 4.09 ct |
| 10mm | 4.76 ct |
| 10.5mm | 5.58 ct |
| 11mm | 6.34 ct |
| 11.5mm | 7.11 ct |
| 12mm | 7.98 ct |
Princess moissanite size chart
| Size | Carat (DEW) |
|---|---|
| 4.5mm | 0.58 ct |
| 5mm | 0.81 ct |
| 5.5mm | 1.06 ct |
| 6mm | 1.56 ct |
| 6.5mm | 1.89 ct |
| 7mm | 2.22 ct |
| 7.5mm | 2.53 ct |
| 8mm | 3.35 ct |
| 8.5mm | 3.93 ct |
| 9mm | 4.24 ct |
| 9.5mm | 5.38 ct |
| 10mm | 6.07 ct |
| 10.5mm | 6.13 ct |
| 11mm | 7.03 ct |
| 11.5mm | 7.98 ct |
| 12mm | 9.14 ct |
| 13mm | 11.15 ct |
| 14mm | 12.35 ct |
| 15mm | 14.19 ct |
| 16mm | 15.63 ct |
| 17mm | 17.25 ct |
| 18mm | 18.72 ct |
Heart moissanite size chart
| Size | Carat (DEW) |
|---|---|
| 5.5mm | 0.64 ct |
| 6mm | 0.83 ct |
| 6.5mm | 1.07 ct |
| 7mm | 1.32 ct |
| 7.5mm | 1.68 ct |
| 8mm | 2.01 ct |
| 8.5mm | 2.32 ct |
| 9mm | 2.87 ct |
| 9.5mm | 3.06 ct |
| 10mm | 3.72 ct |
| 11mm | 4.99 ct |
| 12mm | 6.01 ct |
Marquise moissanite size chart
| Size | Carat (DEW) |
|---|---|
| 8×4mm | 0.55 ct |
| 9×4.5mm | 0.68 ct |
| 10×5mm | 1.11 ct |
| 11×5.5mm | 1.59 ct |
| 12×6mm | 1.86 ct |
| 13×6.5mm | 2.52 ct |
| 14×7mm | 2.87 ct |
Oval moissanite size chart
| Size | Carat (DEW) |
|---|---|
| 6×4mm | 0.54 ct |
| 7×5mm | 0.91 ct |
| 8×6mm | 1.48 ct |
| 9×7mm | 2.16 ct |
| 10×8mm | 3.35 ct |
| 11×9mm | 4.61 ct |
| 12×10mm | 5.94 ct |
| 14×10mm | 7.31 ct |
| 16×12mm | 8.53 ct |
| 18×13mm | 10.06 ct |
Asscher moissanite size chart
| Size | Carat (DEW) |
|---|---|
| 5.5mm | 0.83 ct |
| 6mm | 1.10 ct |
| 6.5mm | 1.41 ct |
| 7mm | 1.72 ct |
| 7.5mm | 2.12 ct |
| 8mm | 2.67 ct |
| 8.5mm | 3.19 ct |
| 9mm | 3.53 ct |
| 9.5mm | 4.24 ct |
| 10mm | 5.06 ct |
Emerald moissanite size chart
| Size | Carat (DEW) |
|---|---|
| 6×4mm | 0.61 ct |
| 7×5mm | 1.06 ct |
| 8×6mm | 1.77 ct |
| 9×7mm | 2.71 ct |
| 10×8mm | 3.91 ct |
| 11×9mm | 5.43 ct |
| 12×10mm | 7.08 ct |
| 14×10mm | 9.13 ct |
Radiant moissanite size chart
| Size | Carat (DEW) |
|---|---|
| 6×4mm | 0.67 ct |
| 7×5mm | 1.17 ct |
| 8×6mm | 1.86 ct |
| 9×7mm | 2.87 ct |
| 10×8mm | 4.17 ct |
| 11×9mm | 5.55 ct |
| 12×10mm | 6.93 ct |
Pear moissanite size chart
| Size | Carat (DEW) |
|---|---|
| 7×5mm | 0.78 ct |
| 8×5mm | 0.92 ct |
| 9×6mm | 1.45 ct |
| 10×7mm | 2.08 ct |
| 10.5×7mm | 2.32 ct |
| 12×8mm | 3.55 ct |
| 14×10mm | 5.47 ct |
| 16×12mm | 7.65 ct |
Choosing a size for your hand
On a typical ring finger of about 17 mm across, a 1 ct round covers a little over a third of the width. On a slimmer finger the same stone looks bigger, and on a broader one smaller. If you're choosing for someone else, look at the rings they already wear. You can also measure their ring size with our South African ring size guide.
Moissanite is priced by weight, not cut, so a 1 ct oval costs the same as a 1 ct round. The price guide lists every size with its price.
How big is a 1 carat moissanite in mm?+
A round moissanite of about 1 ct DEW measures 6.5mm across; an oval of about 1 ct measures 7×5mm. It is the same size as a 1 ct diamond.
What does DEW mean on a moissanite?+
Diamond-equivalent weight: the weight a diamond of the same size would have. Moissanite is about 10% lighter than diamond, so DEW is used to keep sizes comparable.
Does a moissanite look bigger than a diamond of the same carat?+
Sold by DEW, no: a 1 ct DEW moissanite is the same size as a 1 ct diamond. By true weight, a moissanite is about 10% larger than a diamond of the same weight, because it is lighter.
Which moissanite cut looks biggest?+
Elongated cuts look biggest for their weight. The marquise has the largest face-up area of any cut, followed by the pear and oval. Princess and asscher look slightly smaller than a round of the same weight.