When comparing moissanite carat vs diamond carat, many buyers are surprised to learn that these two gemstones do not have the same physical size at the same carat weight. Understanding the moissanite carat vs diamond carat difference is crucial for making an informed purchase, as it directly affects the visual size, appearance, and value of your ring. This guide explains the science behind the size difference, provides detailed comparison tables, and helps you choose the right size regardless of which gemstone you select.
Why Moissanite Carat Differs from Diamond Carat
The Science: Density Difference
The key to understanding moissanite carat vs diamond carat lies in density. Carat is a unit of weight (200 milligrams), not size. Because moissanite and diamond have different chemical compositions and crystal structures, they have different densities:
| Gemstone | Chemical Formula | Density (g/cm³) | Mohs Hardness |
|---|---|---|---|
| Diamond | Carbon (C) | 3.52 | 10.0 |
| Moissanite | Silicon Carbide (SiC) | 3.21 | 9.25 |
Moissanite is approximately 9% less dense than diamond. This means that for the same weight, moissanite occupies more volume—making a moissanite stone physically larger than a diamond of the same carat weight.
What This Means in Practice
- A 1.0-carat moissanite (by actual weight) is physically larger than a 1.0-carat diamond
- A 6.5mm round moissanite weighs approximately 0.88 carats, while a 6.5mm round diamond weighs 1.0 carat
- To get a moissanite that looks the same size as a 1.0-carat diamond, you need a 0.88-carat moissanite
This is why most moissanite retailers sell stones using Diamond Equivalent Weight (DEW)—it allows buyers to compare sizes using familiar diamond measurements.
Moissanite Carat vs Diamond Carat: Size Comparison Table
Round Brilliant Comparison
| Diamond Carat | Diamond Diameter | Moissanite DEW | Moissanite Diameter | Actual Moissanite Weight |
|---|---|---|---|---|
| 0.50 ct | 5.0 mm | 0.50 ct | 5.0 mm | 0.44 ct |
| 0.75 ct | 5.8 mm | 0.75 ct | 5.8 mm | 0.66 ct |
| 1.00 ct | 6.5 mm | 1.00 ct | 6.5 mm | 0.88 ct |
| 1.25 ct | 7.0 mm | 1.25 ct | 7.0 mm | 1.10 ct |
| 1.50 ct | 7.4 mm | 1.50 ct | 7.4 mm | 1.32 ct |
| 2.00 ct | 8.0 mm | 2.00 ct | 8.0 mm | 1.76 ct |
| 2.50 ct | 8.5 mm | 2.50 ct | 8.5 mm | 2.20 ct |
| 3.00 ct | 9.0 mm | 3.00 ct | 9.0 mm | 2.64 ct |
As the table shows, when moissanite is sold by DEW, the visual size (diameter) matches the diamond carat. The actual moissanite weight is approximately 12% less.
Same Actual Weight Comparison
| Actual Weight | Diamond Diameter | Moissanite Diameter | Size Difference |
|---|---|---|---|
| 0.50 ct | 5.0 mm | 5.2 mm | +4% |
| 0.75 ct | 5.8 mm | 6.1 mm | +5% |
| 1.00 ct | 6.5 mm | 6.8 mm | +5% |
| 1.50 ct | 7.4 mm | 7.8 mm | +5% |
| 2.00 ct | 8.0 mm | 8.4 mm | +5% |
| 3.00 ct | 9.0 mm | 9.5 mm | +6% |
When comparing moissanite carat vs diamond carat at the same actual weight, moissanite is approximately 5–6% larger in diameter.
Diamond Equivalent Weight (DEW) Explained
DEW is the standard used by moissanite retailers to help buyers compare sizes. It answers the question: "If this moissanite were a diamond, what carat weight would it be?"
How DEW Works
| Moissanite Actual Weight | Physical Size (mm) | DEW | Diamond Weight at Same Size |
|---|---|---|---|
| 0.44 ct | 5.0 mm | 0.50 ct | 0.50 ct |
| 0.88 ct | 6.5 mm | 1.00 ct | 1.00 ct |
| 1.76 ct | 8.0 mm | 2.00 ct | 2.00 ct |
Why DEW Matters
- Easy comparison: DEW lets you compare moissanite sizes to diamond sizes you may be familiar with
- Consistent retail standard: All major moissanite retailers use DEW
- Visual accuracy: A 1.0 DEW moissanite looks the same size as a 1.0-carat diamond
Potential Confusion
Some buyers worry that DEW is misleading, but it is simply a size reference, not a quality claim. The important thing is to understand that DEW represents visual size, not actual weight. Always check the millimeter dimensions for the most accurate comparison. Use our moissanite size chart for precise measurements.
Moissanite Carat vs Diamond Carat: Price Comparison
The size difference is only part of the story. The price difference is even more dramatic:
| Size (DEW) | Moissanite Price (Colorless) | Diamond Price (G/VS) | Savings |
|---|---|---|---|
| 1.00 ct | 600 | 8,000 | 85–93% |
| 1.50 ct | 900 | 15,000 | 87–94% |
| 2.00 ct | 1,300 | 25,000 | 90–95% |
| 3.00 ct | 2,500 | 60,000 | 95–97% |
At larger sizes, the savings become even more dramatic because diamond prices increase exponentially with carat weight, while moissanite prices increase more linearly.
How the Size Difference Affects Appearance
Brilliance and Fire
While moissanite carat vs diamond carat differs in physical size, both gemstones have exceptional optical properties:
| Property | Moissanite | Diamond |
|---|---|---|
| Refractive Index | 2.65 | 2.42 |
| Dispersion (Fire) | 0.104 | 0.044 |
| Brillillion | Higher | High |
Moissanite's higher refractive index means it produces more brilliance (white sparkle) and more fire (colorful sparkle) than diamond. This means a moissanite stone may appear even more eye-catching than a diamond of the same visual size.
Color Differences at Larger Sizes
One consideration in the moissanite carat vs diamond carat comparison is color. Larger moissanite stones (2+ carats) can sometimes show slight body color or tint, especially in near-colorless grades. If you are buying a larger stone, consider upgrading to colorless (D–E–F equivalent) moissanite for the most diamond-like appearance.
Frequently Asked Questions: Moissanite Carat vs Diamond Carat
Is a 1 carat moissanite the same size as a 1 carat diamond?
If the moissanite is sold as "1.0 ct DEW," then yes—it is the same visual size as a 1.0-carat diamond (6.5mm diameter for round brilliant). However, the actual moissanite weight is approximately 0.88 carats due to the density difference. Learn more in our 1 carat moissanite guide.
Why is moissanite lighter than diamond?
Moissanite is made of silicon carbide (SiC), which has a lower density (3.21 g/cm³) than diamond's carbon crystal (3.52 g/cm³). This means moissanite is less dense and occupies more volume per unit of weight.
Does the size difference make moissanite a better value?
Yes. Because moissanite is less dense, you get a larger stone per carat of actual weight. Combined with the dramatically lower price per carat, moissanite offers exceptional value—especially at larger sizes.
Can a jeweler tell the difference between moissanite and diamond?
Yes. Professional jewelers can distinguish moissanite from diamond using specialized tools. Moissanite conducts electricity (diamond does not), and it has different optical properties. However, to the naked eye, high-quality colorless moissanite is very difficult to distinguish from diamond.
Should I buy moissanite by actual weight or DEW?
Most retailers sell by DEW because it is more useful for buyers comparing to diamond sizes. However, always check the millimeter dimensions to understand the actual visual size. For more on this, see our complete moissanite carat size guide.
Conclusion
The moissanite carat vs diamond carat difference comes down to one key factor: density. Moissanite is approximately 9% less dense than diamond, meaning it is physically larger at the same carat weight. This is why the industry uses Diamond Equivalent Weight (DEW) to express moissanite sizes in terms buyers can easily understand.
When you buy a 1.0 DEW moissanite, you get a stone that looks the same size as a 1.0-carat diamond—but costs 85–90% less. At larger sizes, the value proposition becomes even more compelling. Understanding this difference empowers you to make an informed decision and get the most stone for your budget.
Ready to explore specific sizes? Check our moissanite size chart, learn about 1 carat, 2 carat, and 3 carat options, and find your perfect ring today.