Why are moissanite rings usually sized in “mm” rather than “ct”? Should you pay more attention to “mm” or “ct”? And is a 1-carat moissanite the same size as a 1-carat diamond?
This guide details the relationship between size and carat weight, their differences, and the moissanite mm to carat weight conversion. (Including actual carat weight and diamond equivalent weight.)
Millimeters (mm) vs. Carats (ct)
To understand the difference between millimeters (mm) and carats (ct), we need to look at what each unit actually measures.
“Mm” refers to the gemstone’s face size (diameter), while carat (1ct = 0.2g) measures its weight.
In other words, carat measures weight, and millimeter measures size — the former determines the price, while the latter determines the visual appearance.
For most buyers, millimeters are often a more intuitive way to compare stones because they directly reflect how large the gemstone will look when worn. However, from a valuation standpoint, carat weight is still an important metric. That’s why both size and weight should be considered when choosing a gemstone.
The unit “carat” was originally created to measure the weight of diamonds. Over time, people began using carats to describe the weight of other gemstones as well.
However, because different gemstones have different densities (specific gravities), two gems with the same carat weight can look different in size.
To make it easier for consumers to compare other gemstones to diamonds visually, the concept of Diamond Equivalent Weight (DEW) was introduced. DEW is not the gem’s actual weight — it represents how large the gemstone appears compared to a diamond of a certain carat weight.
For example:
Moissanite has a density of 3.22, while diamond’s density is 3.52. That means moissanite is about 8.5% lighter than diamond. So, for the same size, moissanite’s actual carat weight (ACW) will always be slightly lower than a diamond’s.
A 6.5mm moissanite, for instance, weighs about 0.9ct but looks the same size as a 1ct diamond.
(Approximate formula: Moissanite ACW ≈ Diamond DEW × (3.22 / 3.52))
Now that you understand the basics, let’s look at how different moissanite cuts compare in terms of millimeter size (mm), actual carat weight (ACW), and diamond equivalent weight (DEW).
Moissanite Mm to Carat Conversion Charts (Including DEW)
Keep in mind that mm-to-carat conversions are only approximate, not exact.
The tables below show the estimated weight range of moissanite across various shapes and sizes, including both actual carat weight (ACW) and diamond equivalent weight (DEW).
These values are based on industry-standard cutting proportions — meaning typical table sizes and depth ratios.
If a gemstone deviates from these proportions — for instance, if it has a larger table, shallower crown, or deeper pavilion — its total volume and weight will change.
As a result, even if two stones have the same millimeter size, their visual appearance and carat weight may differ.
In short:
Mm determines visual size, carats reflect actual weight, and the cut proportions balance the two.
Round Moissanite Size Chart: mm to Carat (ACW vs. DEW)
| Moissanite Size | Actual Carat Weight | Diamond Equivalent Weight |
|---|---|---|
| 3mm | 0.09ct | 0.10ct |
| 4mm | 0.23ct | 0.25ct |
| 4.5mm | 0.26ct | 0.28ct |
| 5mm | 0.46ct | 0.50ct |
| 5.5mm | 0.60ct | 0.66ct |
| 6mm | 0.78ct | 0.85ct |
| 6.5mm | 0.91ct | 1.00ct |
| 7mm | 1.19ct | 1.30ct |
| 7.5mm | 1.53ct | 1.67ct |
| 8mm | 1.83ct | 2.00ct |
| 8.5mm | 2.22ct | 2.43ct |
| 9mm | 2.52ct | 2.75ct |
| 9.5mm | 3.06ct | 3.35ct |
| 10mm | 3.52ct | 3.85ct |
Oval Moissanite Size Chart: mm to Carat (ACW vs. DEW)
| Moissanite Size | Actual Carat Weight | Diamond Equivalent Weight |
|---|---|---|
| 4x3mm | 0.14ct | 0.15ct |
| 6x4mm | 0.46ct | 0.50ct |
| 7x5mm | 0.69ct | 0.75ct |
| 7.7×5.57mm | 0.91ct | 1.00ct |
| 8x6mm | 1.14ct | 1.25ct |
| 8.5×6.5mm | 1.37ct | 1.50ct |
| 9×6.5mm | 1.60ct | 1.75ct |
| 9x7mm | 1.83ct | 2.00ct |
| 10x8mm | 2.29ct | 2.50ct |
| 12x8mm | 2.74ct | 3.00ct |
| 12×8.5mm | 3.20ct | 3.50ct |
| 11x9mm | 3.52ct | 3.85ct |
| 12.5×8.5mm | 3.66ct | 4.00ct |
Emerald Cut Moissanite Size Chart: mm to Carat (ACW vs. DEW)
| Moissanite Size | Actual Carat Weight | Diamond Equivalent Weight |
|---|---|---|
| 6x4mm | 0.46ct | 0.50ct |
| 7x5mm | 0.91ct | 1.00ct |
| 8x6mm | 1.60ct | 1.75ct |
| 9x6mm | 1.83ct | 2.00ct |
| 9x7mm | 2.29ct | 2.50ct |
| 10x7mm | 2.84ct | 3.10ct |
| 10x8mm | 3.66ct | 4.00ct |
👉 Shop Emerald Cut Moissanite Rings
Pear Moissanite Size Chart: mm to Carat (ACW vs. DEW)
| Moissanite Size | Actual Carat Weight | Diamond Equivalent Weight |
|---|---|---|
| 6x4mm | 0.46ct | 0.50ct |
| 7x5mm | 0.69ct | 0.75ct |
| 8x5mm | 0.91ct | 1.00ct |
| 8x6mm | 1.14ct | 1.25ct |
| 9x6mm | 1.23ct | 1.35ct |
| 9x7mm | 1.83ct | 2.00ct |
| 10x7mm | 1.92ct | 2.10ct |
| 10x8mm | 2.29ct | 2.50ct |
| 12x8mm | 2.74ct | 3.00ct |
Cushion Moissanite Size Chart: mm to Carat (ACW vs. DEW)
| Moissanite Size | Actual Carat Weight | Diamond Equivalent Weight |
|---|---|---|
| 4mm | 0.23ct | 0.25ct |
| 5mm | 0.69ct | 0.75ct |
| 5.5mm | 0.91ct | 1.00ct |
| 6mm | 1.05ct | 1.15ct |
| 6.5mm | 1.37ct | 1.50ct |
| 7mm | 1.60ct | 1.75ct |
| 7.5mm | 2.06ct | 2.25ct |
| 8mm | 2.29ct | 2.50ct |
| 8.5mm | 2.74ct | 3.00ct |
| 9mm | 3.66ct | 4.00ct |
| 9.5mm | 4.12ct | 4.50ct |
| 10mm | 4.57ct | 5.00ct |
👉 Shop Cushion Moissanite Rings
Radiant Moissanite Size Chart: mm to Carat (ACW vs. DEW)
| Moissanite Size | Actual Carat Weight | Diamond Equivalent Weight |
|---|---|---|
| 6x4mm | 0.46ct | 0.50ct |
| 7x5mm | 0.91ct | 1.00ct |
| 8x6mm | 1.60ct | 1.75ct |
| 8.5×6.5mm | 1.83ct | 2.00ct |
| 9x7mm | 2.74ct | 3.00ct |
| 10x8mm | 3.66ct | 4.00ct |
👉 Shop Radiant Moissanite Rings
Marquise Moissanite Size Chart: mm to Carat (ACW vs. DEW)
| Moissanite Size | Actual Carat Weight | Diamond Equivalent Weight |
|---|---|---|
| 6x3mm | 0.23ct | 0.25ct |
| 8x4mm | 0.46ct | 0.50ct |
| 10x5mm | 0.91ct | 1.00ct |
| 12x6mm | 1.37ct | 1.50ct |
| 13×6.5mm | 1.83ct | 2.00ct |
| 14x7mm | 2.29ct | 2.50ct |
| 15x7mm | 2.74ct | 3.00ct |
| 15x8mm | 3.20ct | 3.50ct |
👉 Shop Marquise Moissanite Rings
Princess Cut Moissanite Size Chart: mm to Carat (ACW vs. DEW)
| Moissanite Size | Actual Carat Weight | Diamond Equivalent Weight |
|---|---|---|
| 4mm | 0.36ct | 0.39ct |
| 5mm | 0.69ct | 0.75ct |
| 5.5mm | 0.91ct | 1.00ct |
| 6mm | 1.14ct | 1.25ct |
| 6.5mm | 1.27ct | 1.39ct |
| 7mm | 1.83ct | 2.00ct |
| 7.5mm | 2.29ct | 2.50ct |
| 8mm | 2.74ct | 3.00ct |
| 8.5mm | 3.20ct | 3.50ct |
| 8.75mm | 3.66ct | 4.00ct |
| 9mm | 4.12ct | 4.50ct |
| 9.5mm | 4.57ct | 5.00ct |
| 10mm | 5.14ct | 5.62ct |
👉 Shop Princess Cut Moissanite Rings
Kite Cut Moissanite Size Chart: mm to Carat (ACW vs. DEW)
| Moissanite Size | Actual Carat Weight | Diamond Equivalent Weight |
|---|---|---|
| 4x2mm | 0.05ct | 0.05ct |
| 5x3mm | 0.13ct | 0.14ct |
| 8x4mm | 0.38ct | 0.42ct |
| 9x6mm | 0.91ct | 1.00ct |
| 10x7mm | 1.28ct | 1.40ct |
| 12x8mm | 1.92ct | 2.10ct |
👉 Shop Kite Cut Moissanite Rings
Hexagon Moissanite Size Chart: mm to Carat (ACW vs. DEW)
Hexagons come in regular hexagon and elongated hexagon shapes, and their common sizes correspond to the following carat weights:
| Moissanite Size | Actual Carat Weight | Diamond Equivalent Weight |
|---|---|---|
| 6mm | 0.91ct | 1.00ct |
| 7mm | 1.37ct | 1.50ct |
| 8mm | 2.38ct | 2.60ct |
| 10x5mm | 1.37ct | 1.50ct |
👉 Shop Hexagon Moissanite Rings
When choosing a moissanite, there’s no need to worry about matching the carat weight exactly to a diamond. The mm size is the most intuitive reference, helping you quickly gauge how the ring will look when worn. Explore our Moissanite Engagement Rings collection to find your perfect match.
Moissanite Mm to Carat FAQs
According to international standards, 1 carat is exactly 200 milligrams (0.2 grams), or 100 points. The weight of moissanite follows the same measurement standard.
Approximate sizes (standard cut): Round 5mm, Oval 6×4mm / Pear: 6×4mm / Princess 5mm / Marquise 8×4mm.
Approximate sizes (standard cut): Round 6.5mm / Oval 7×5mm / Pear 8×6mm / Marquise 10×5mm / Princess 6mm / Hexagon 6mm / Heart 6.5mm.
Approximate sizes (standard cut): Round 8 mm / Oval 8×6 mm / Pear 9×6 mm / Cushion 7 mm / Princess 6.5 mm / Hexagon 7 mm / Kite 10×7 mm.
Approximate sizes (standard cut): Round 8mm / Oval 9×7mm / Pear 10×7mm / Emerald 9×6mm / Princess 7mm / Kite 12×8mm / Coffin 10×7mm
Approximate sizes (standard cut): Round: 9 mm / Oval 10×8mm / Pear 12×8mm / Marquise: 14×7mm / Emerald 10×7mm / Radiant 10×7mm / Elongated Cushion 9×7mm / Princess 8mm