Moissanite & diamond size chart.
Stones look bigger or smaller depending on their cut and millimetre size โ not their carat weight. Use the chart below to find the millimetre size that matches the look you want.
Moissanite & diamond size chart.
Compare the millimetre size of a stone to its carat weight โ moissanite weighs less than a diamond of the same size, so we always recommend choosing by mm.
Round
The most popular cut โ maximum brilliance from any angle. Mapple Gems rounds are precision-cut for ideal proportions.
| Size (mm) | Moissanite (ct) | Diamond (ct) |
|---|---|---|
| 5.0 | 0.50 | 0.50 |
| 5.5 | 0.62 | 0.67 |
| 6.0 | 0.75 | 0.84 |
| 6.5 | 0.92 | 1.00 |
| 7.0 | 1.15 | 1.30 |
| 7.5 | 1.40 | 1.50 |
| 8.0 | 1.80 | 2.00 |
| 8.5 | 2.15 | 2.40 |
| 9.0 | 2.50 | 3.00 |
| 9.5 | 2.85 | 3.40 |
| 10.0 | 3.50 | 4.00 |
| 10.5 | 4.10 | 4.60 |
| 11.0 | 4.80 | 5.40 |
| 11.5 | 5.50 | 6.00 |
| 12.0 | 6.20 | 6.85 |
| 12.5 | 6.85 | 7.50 |
| 13.0 | 7.85 | 8.50 |
| 13.5 | 8.80 | 9.50 |
| 14.0 | 10.00 | 10.80 |
Oval
Elongates the finger; a finger-flattering classic. Sizes are listed as LรW in millimetres.
| Size (mm) | Moissanite (ct) | Diamond (ct) |
|---|---|---|
| 6x4 | 0.50 | 0.65 |
| 7x5 | 0.75 | 1.00 |
| 8x6 | 1.25 | 1.50 |
| 9x7 | 1.80 | 2.20 |
| 10x8 | 2.30 | 2.85 |
| 11x9 | 2.95 | 3.60 |
| 12x9 | 3.40 | 4.00 |
| 12x10 | 3.85 | 4.65 |
| 13x10 | 4.30 | 5.00 |
| 14x10 | 4.90 | 5.50 |
| 14x11 | 5.50 | 6.20 |
| 15x12 | 6.50 | 7.50 |
| 16x12 | 7.50 | 8.50 |
| 17x13 | 8.50 | 9.50 |
| 18x13 | 10.00 | 11.00 |
Cushion
Vintage romance with modern brilliance. A timeless square-with-rounded-corners look.
| Size (mm) | Moissanite (ct) | Diamond (ct) |
|---|---|---|
| 5.0 | 0.50 | 0.55 |
| 6.0 | 0.90 | 1.00 |
| 6.5 | 1.15 | 1.30 |
| 7.0 | 1.50 | 1.70 |
| 7.5 | 1.85 | 2.15 |
| 8.0 | 2.40 | 2.75 |
| 9.0 | 3.30 | 3.90 |
| 10.0 | 4.40 | 5.20 |
| 11.0 | 5.80 | 6.80 |
| 12.0 | 7.50 | 8.80 |
| 13.0 | 9.00 | 10.50 |
| 13.5 | 10.00 | 11.50 |
Emerald
Hall-of-mirrors clarity with elegant step-cut facets. Sizes are LรW.
| Size (mm) | Moissanite (ct) | Diamond (ct) |
|---|---|---|
| 6x4 | 0.50 | 0.65 |
| 7x5 | 0.80 | 1.00 |
| 8x6 | 1.40 | 1.75 |
| 9x7 | 1.90 | 2.25 |
| 10x8 | 2.50 | 3.00 |
| 11x9 | 3.30 | 4.00 |
| 12x10 | 4.20 | 5.00 |
| 13x10 | 4.80 | 5.50 |
| 14x10 | 5.50 | 6.50 |
| 15x11 | 6.80 | 7.80 |
| 16x12 | 8.20 | 9.50 |
| 17x13 | 10.00 | 11.50 |
Radiant
Brilliant-cut facets in an emerald silhouette โ fire and sparkle in one. Sizes are LรW.
| Size (mm) | Moissanite (ct) | Diamond (ct) |
|---|---|---|
| 6x4 | 0.50 | 0.65 |
| 7x5 | 0.80 | 1.00 |
| 8x6 | 1.40 | 1.75 |
| 9x7 | 1.90 | 2.25 |
| 10x8 | 2.50 | 3.00 |
| 11x9 | 3.10 | 3.75 |
| 12x10 | 4.20 | 5.00 |
| 13x10 | 4.60 | 5.50 |
| 14x10 | 5.20 | 6.20 |
| 15x11 | 6.50 | 7.50 |
| 16x12 | 8.00 | 9.00 |
| 17x13 | 10.00 | 11.50 |
Pear
A romantic teardrop โ modern, distinctive, and beautifully finger-elongating. Sizes are LรW.
| Size (mm) | Moissanite (ct) | Diamond (ct) |
|---|---|---|
| 6x4 | 0.50 | 0.55 |
| 7x5 | 0.75 | 0.85 |
| 8x6 | 1.20 | 1.50 |
| 9x6 | 1.50 | 1.75 |
| 10x7 | 1.90 | 2.25 |
| 11x7 | 2.40 | 2.85 |
| 12x8 | 3.10 | 3.60 |
| 13x9 | 3.90 | 4.50 |
| 14x9 | 4.50 | 5.30 |
| 15x10 | 5.50 | 6.50 |
| 16x10 | 6.50 | 7.50 |
| 17x11 | 7.85 | 9.00 |
| 18x12 | 10.00 | 11.50 |
Marquise
Maximum mm presence per carat โ the most finger-coverage of any cut. Sizes are LรW.
| Size (mm) | Moissanite (ct) | Diamond (ct) |
|---|---|---|
| 7x4 | 0.50 | 0.65 |
| 8x4 | 0.75 | 0.95 |
| 8.5x4.5 | 1.00 | 1.20 |
| 9x4.5 | 1.20 | 1.40 |
| 10x5 | 1.50 | 1.75 |
| 11x6 | 2.05 | 2.40 |
| 12x6 | 2.50 | 3.00 |
| 13x6.5 | 3.10 | 3.65 |
| 14x7 | 3.50 | 4.20 |
| 15x8 | 4.50 | 5.30 |
| 16x8 | 5.20 | 6.00 |
| 17x8.5 | 6.20 | 7.40 |
| 18x9 | 7.20 | 8.50 |
| 19x9.5 | 8.50 | 10.00 |
| 20x10 | 10.00 | 11.80 |
Princess
Sharp, modern, square-cut brilliance โ a contemporary classic.
| Size (mm) | Moissanite (ct) | Diamond (ct) |
|---|---|---|
| 4.5 | 0.50 | 0.55 |
| 5.0 | 0.60 | 0.70 |
| 5.5 | 0.80 | 1.00 |
| 6.0 | 1.05 | 1.25 |
| 6.5 | 1.35 | 1.60 |
| 7.0 | 1.65 | 2.00 |
| 7.5 | 2.05 | 2.50 |
| 8.0 | 2.50 | 3.00 |
| 8.5 | 3.05 | 3.50 |
| 9.0 | 3.70 | 4.40 |
| 9.5 | 4.30 | 5.00 |
| 10.0 | 5.00 | 5.80 |
| 10.5 | 5.80 | 6.80 |
| 11.0 | 6.60 | 7.80 |
| 11.5 | 7.50 | 8.80 |
| 12.0 | 8.50 | 10.00 |
| 12.5 | 10.00 | 11.50 |
Asscher
Art Deco geometry โ concentric step-cut facets in a perfect square.
| Size (mm) | Moissanite (ct) | Diamond (ct) |
|---|---|---|
| 4.5 | 0.50 | 0.65 |
| 5.0 | 0.60 | 0.75 |
| 5.5 | 0.80 | 1.00 |
| 6.0 | 1.05 | 1.30 |
| 6.5 | 1.40 | 1.70 |
| 7.0 | 1.80 | 2.20 |
| 7.5 | 2.30 | 2.75 |
| 8.0 | 2.85 | 3.40 |
| 8.5 | 3.50 | 4.20 |
| 9.0 | 4.20 | 5.00 |
| 9.5 | 5.00 | 6.00 |
| 10.0 | 5.80 | 7.00 |
| 10.5 | 6.80 | 8.00 |
| 11.0 | 8.00 | 9.50 |
| 12.0 | 10.00 | 12.00 |
Carat weights are approximate โ actual weight varies by cut and finish. Email mapplegems@gmail.com if you need an exact stone match.
Sizing questions.
Why does moissanite weigh less than a diamond of the same size?
Moissanite is about 15% less dense than diamond. So a 7.5 mm round moissanite weighs roughly 1.40 ct, while a 7.5 mm round diamond weighs roughly 1.50 ct โ same visible size, slightly less carat weight.
That's why we always recommend choosing by millimetres, not carats.
Are lab-grown diamonds real diamonds?
Yes โ lab-grown diamonds are chemically, optically, and physically identical to mined diamonds. The only difference is how they're made. See the full comparison โ
How do I know what size will look right on my finger?
As a rough guide: a 6.5 mm round (~1 ct) looks classic on most fingers; 7.0โ7.5 mm reads as a noticeable statement; 8.0 mm and up reads as bold. Email mapplegems@gmail.com with your ring size and we'll send a comparison.
Why does my stone look smaller than I expected?
Two stones with the same carat weight can look very different in size depending on the cut quality โ a deeply cut stone hides carat weight underneath. We only cut to ideal proportions, so our mm measurements give you the size you actually see.
Can you cut a custom size that isn't on the chart?
Yes โ for custom designs we can source or cut almost any size and shape combination. Submit your details via the Custom Design form and our atelier will respond within 1โ2 business days.
We'll size it with you.
Tell us your ring size and the look you're going for โ we'll recommend the exact mm size and stone shape to match. Email mapplegems@gmail.com.