Moissanite carat size chart: how big is 1, 2 or 3 carats in mm?
A 1 carat round moissanite is about 6.5 mm across, the same as a 1 carat diamond, because moissanite is usually sold by "diamond equivalent weight": the size a diamond of that carat would be. Moissanite is lighter (specific gravity 3.22 against 3.52), so a 6.5 mm stone actually weighs roughly 0.9 carat. The chart below gives the usual round and oval sizes; treat every figure as approximate, since cut proportions vary.
Why moissanite carats are "diamond equivalent"
Carat is a weight (0.2 grams), not a size. Moissanite is about 9% less dense than diamond, so a moissanite of the same diameter weighs less. Sellers quote the diamond equivalent so shoppers can compare sizes directly; a "2 carat" moissanite is an 8 mm stone that looks like a 2 carat diamond.
How to use the chart
For studs, the per-stone size is what matters: "1 ct total" earrings are two stones of about 5.2 mm. For rings, measure an existing ring you like with a ruler across the stone, then match the millimetres, not the carats.
| Carat (DEW) | Round (mm) | Oval (mm) | Shop |
|---|---|---|---|
| 0.25 ct | 4.1 | 5 x 3 | Studs |
| 0.5 ct | 5.2 | 6 x 4 | Studs |
| 0.75 ct | 5.8 | 7 x 5 | Studs |
| 1 ct | 6.5 | 8 x 6 | Rings |
| 1.5 ct | 7.4 | 9 x 7 | Rings |
| 2 ct | 8.0 | 10 x 7.5 | Rings |
| 2.5 ct | 8.8 | 10 x 8 | Rings |
| 3 ct | 9.3 | 11 x 9 | Rings |
| 4 ct | 10.2 | 12 x 10 | Rings |
| 5 ct | 11.0 | 13 x 10 | Rings |
Frequently Asked Questions
How big is a 1 carat moissanite?
About 6.5 mm across for a round stone, the same diameter as a 1 carat diamond, because moissanite is sold by diamond equivalent weight.
Why does my moissanite weigh less than the listed carat?
Because the listing uses diamond equivalent weight. Moissanite is lighter than diamond, so a stone the size of a 1 carat diamond weighs about 0.9 carat.
What size moissanite looks best in a ring?
1 to 2 carats (about 6.5 to 8 mm round) suits most hands. Larger stones look bold; moissanite's low price makes them tempting, so hold the size up against your finger before ordering.
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