Moissanite Size Chart: MM to Carat Conversion
Every chart on this page is the one we use in our own workshop in Surat. It exists because the single most confusing thing about buying moissanite is that the industry sells it by millimeter size while talking about it in carats, and nobody explains the conversion honestly.
First, the honest part: what DEW means
Moissanite is about 9% less dense than diamond. A 6.5mm round diamond weighs 1.00 carat. A 6.5mm round moissanite, the identical size on your hand, weighs about 0.91 carats.
So the industry, including us, sells moissanite by DEW, diamond equivalent weight. When a listing says 1ct moissanite, it means the stone is the size a 1ct diamond would be, not that it weighs 1.00 carat on a scale. The stone in that listing is 6.5mm across and weighs roughly 0.91ct.
This is standard practice and not a scam, but you should know it before you weigh a loose stone and wonder why the number comes up short. Size on the hand is what DEW preserves, and size on the hand is what you are actually buying.
Round moissanite: mm to carat (DEW)
| Diameter (mm) | Carat (DEW) | Actual moissanite weight |
|---|---|---|
| 4.0 mm | 0.25 ct | ~0.23 ct |
| 4.5 mm | 0.36 ct | ~0.33 ct |
| 5.0 mm | 0.50 ct | ~0.46 ct |
| 5.5 mm | 0.66 ct | ~0.60 ct |
| 6.0 mm | 0.84 ct | ~0.77 ct |
| 6.5 mm | 1.00 ct | ~0.91 ct |
| 7.0 mm | 1.25 ct | ~1.14 ct |
| 7.5 mm | 1.60 ct | ~1.46 ct |
| 8.0 mm | 2.00 ct | ~1.82 ct |
| 8.5 mm | 2.35 ct | ~2.14 ct |
| 9.0 mm | 2.75 ct | ~2.51 ct |
| 9.5 mm | 3.35 ct | ~3.05 ct |
| 10.0 mm | 3.87 ct | ~3.53 ct |
| 11.0 mm | 4.91 ct | ~4.48 ct |
Fancy shapes: what a 1ct DEW stone measures
Elongated shapes spread their weight across the finger, so the same DEW looks larger in an oval or marquise than in a round. These are the typical measurements for a 1ct DEW stone in each shape.
| Shape | 1 ct measures about | 2 ct measures about |
|---|---|---|
| Round | 6.5 mm | 8.0 mm |
| Oval | 7.5 x 5.5 mm | 9 x 7 mm |
| Cushion | 6.0 x 6.0 mm | 7.5 x 7.5 mm |
| Princess | 5.5 x 5.5 mm | 7.0 x 7.0 mm |
| Emerald | 7.0 x 5.0 mm | 8.5 x 6.5 mm |
| Radiant | 6.0 x 6.0 mm | 7.5 x 7.0 mm |
| Pear | 8.0 x 5.5 mm | 10 x 7 mm |
| Marquise | 10 x 5 mm | 12.5 x 6.5 mm |
| Asscher | 5.5 x 5.5 mm | 7.0 x 7.0 mm |
| Heart | 6.5 x 6.5 mm | 8.0 x 8.0 mm |
Measurements vary slightly with cutting proportions. A deep-cut stone hides weight underneath where you cannot see it, a shallow one spreads it. Treat the table as a reliable guide rather than a guarantee to the tenth of a millimeter.
Common conversions people ask us
| Question | Answer |
|---|---|
| What size moissanite is 2 carat? | 8.0 mm in a round. About 9 x 7 mm in an oval. |
| How big is 5 mm moissanite in carats? | 0.50 ct DEW in a round. |
| How big is 6 mm moissanite in carats? | 0.84 ct DEW in a round, commonly sold as 0.80 ct. |
| How big is 10 mm moissanite in carats? | Just under 4 ct DEW in a round. |
| What is 7 x 5 mm in carats? | Roughly 1 ct DEW in an oval or emerald cut. |
| What is 8 x 6 mm in carats? | Roughly 1.5 ct DEW in an oval, closer to 1.75 in a cushion. |
How to choose a size without regretting it
Two rules from watching real orders. First, finger size changes how a stone reads: 6.5mm on a size 4.5 finger looks substantial, and the same stone on a size 8.5 finger looks modest. Second, moissanite's extra fire becomes visible above roughly 1.5 to 2 carats in bright light, so if you want the least conspicuous stone, stay at or under 1.5 ct DEW. Bigger is not automatically better with this material, and we say that as the people selling it.
Prefer a printable version? The PDF size chart is the same data. And if you know your size, every ring we make is available in it: start with our moissanite engagement rings, or read the complete moissanite guide if you are still deciding whether the stone is right for you.