20% OFF SITEWIDE — JUST ONE ITEM TO SAVE!

MADE TO ORDER - SHIPS IN 14-21 BUSINESS DAYS

Expertise you can trust: The Juyoyo team, a handcrafted fine jewelry brand specializing in gemstones and precious metals, created this article to share practical, research-based insights drawn from years of hands-on experience in jewelry design, material selection, and quality evaluation, helping readers better understand jewelry craftsmanship, materials, value, and care.

Moissanite Carat & Size Guide: mm to Carat Chart & Diamond Comparison

Dec 31,2025 | Juyoyo

moissanite carat and size guide mm to carat

Confused because a moissanite and a diamond of the same size have different carat weights? You’re not alone. Moissanite is lighter than diamonds, so gemstones of the same weight will have different physical sizes. To find the perfect fit, shop by millimeter (mm) size or Diamond Equivalent Weight (DEW) rather than by actual weight.

This guide clarifies the confusion with easy-to-understand charts that convert millimeters to carats. It also explains the crucial concept of Diamond Equivalent Weight (DEW) and provides visual comparisons to help you choose the perfect moissanite with confidence.

Understanding Moissanite Carats, Millimeters, and DEW

Moissanite size confusion comes from mixing up weight and visual size. Knowing the difference between carat, millimeter, and DEW will help you choose a stone that looks exactly the way you expect.

What Is Carat & What Is Millimeter?

A carat is a unit of weight; one carat equals 200 milligrams. It measures how heavy a stone is, not how big it appears on your finger. This distinction is important when comparing moissanite and diamonds.

A millimeter (mm) measures a gemstone’s face-up diameter, which directly affects its visual size, how much of your finger it covers, and its ability to make your hand look longer. When shoppers say a ring looks "bigger" or "smaller," they are almost always reacting to millimeter size, not carat weight.

For moissanite, millimeter size matters more than carat weight when it comes to appearance, especially for everyday engagement rings.

Why Moissanite Carat ≠ Diamond Carat?

Moissanite and diamonds have different densities, which changes how much they weigh at the same size. Diamonds are denser than moissanite, meaning a diamond of identical millimeter dimensions weighs more than a moissanite.

On average, moissanite is 10-18% lighter than a diamond of the same millimeter size, depending on the cut and proportions. A 6.5-millimeter round moissanite does not weigh the same as a 6.5-millimeter round diamond, even though they appear nearly identical in size.

Using Actual Carat Weight (ACW) alone can be misleading because you might end up with a stone that looks much larger or smaller than intended.

What Does DEW (Diamond Equivalent Weight) Mean?

Diamond Equivalent Weight (DEW) is the standard used to describe the visual size of a moissanite gemstone. It answers the question: "What diamond carat size does this moissanite look like?"

For instance, a 6.5-millimeter round moissanite may have an ACW of around 0.91 carats, but its DEW is approximately 1.0 carats because its face-up size matches that of a 1-carat diamond.

At Juyoyo, we recommend using DEW to judge appearance.

Millimeter size to judge the appearance
DEW to compare against diamond expectations
ACW is mainly used for gemological reference.

Moissanite Size Chart: MM to Carat (ACW & DEW)

Always compare moissanite by millimeter size first, not by weight alone. The charts below translate millimeters into the stone’s actual weight and diamond-equivalent visual size. This allows you to shop based on appearance rather than just a number.

Round Cut Moissanite Size Chart

The round brilliant cut is the gold standard for sparkle. Because it is symmetrical, the millimeter-to-carat conversion is consistent.

MM Size	Actual Carat Approx (ACW)	Diamond Equivalent Weight (DEW)
3.0 mm	~0.09 ct	~0.10 ct
4.0 mm	~0.23 ct	~0.25 ct
5.0 mm	~0.46 ct	~0.50 ct
5.5 mm	~0.60 ct	~0.66 ct
6.0 mm	~0.78 ct	~0.85 ct
6.5 mm	~0.91 ct	~1.00 ct
7.0 mm	~1.19 ct	~1.30 ct
7.5 mm	~1.53 ct	~1.67 ct
8.0 mm	~1.83 ct	~2.00 ct

The most popular engagement ring sizes are between 6.0 and 7.0 millimeters, striking a balance between presence, comfort, and everyday wearability.

Fancy shapes, such as oval, pear, and cushion, often appear larger than rounds of the same carat weight because of their elongated surface area.

Oval Moissanite Carat Size Chart

MM Size	Actual Carat Approx (ACW)	Diamond Equivalent Weight (DEW)
5×3 mm	~0.14 ct	~0.15 ct
6×4 mm	~0.46 ct	~0.50 ct
7×5 mm	~0.69 ct	~0.75 ct
7.7×5.57 mm	~0.91 ct	~1.00 ct
8×6 mm	~1.14 ct	~1.25 ct
8.5×6.5 mm	~1.37 ct	~1.50 ct
9×6.5 mm	~1.60 ct	~1.75 ct
9×7 mm	~1.83 ct	~2.00 ct
10×8 mm	~2.29 ct	~2.50 ct

Pear Cut Moissanite Carat Size Chart

MM Size	Actual Carat Approx (ACW)	Diamond Equivalent Weight (DEW)
7 × 5 mm	~0.85 ct	~1.00 ct
8 × 5 mm	~1.05 ct	~1.25 ct
9 × 6 mm	~1.40 ct	~1.60 ct
10 × 7 mm	~2.05 ct	~2.30 ct
11 × 7 mm	~2.45 ct	~2.75 ct
12 × 8 mm	~3.10 ct	~3.50 ct

Cushion Cut Moissanite Carat Size Chart

MM Size	Actual Carat Approx (ACW)	Diamond Equivalent Weight (DEW)
4.0 mm	~0.23 ct	~0.25 ct
5.0 mm	~0.69 ct	~0.75 ct
5.5 mm	~0.91 ct	~1.00 ct
6.0 mm	~1.05 ct	~1.15 ct
6.5 mm	~1.37 ct	~1.50 ct
7.0 mm	~1.60 ct	~1.75 ct
7.5 mm	~2.06 ct	~2.25 ct
8.0 mm	~2.29 ct	~2.50 ct
9.0 mm	~3.66 ct	~4.00 ct

Visual Reference: What Moissanite Carat Sizes Look Like on the Hand

Seeing the size helps bridge the gap between numbers and real-life wear.

The “Sweet Spot” for Engagement Rings

For many, the ideal moissanite engagement ring size falls within the 1.5- to 2.0-carat DEW range (approximately 7.0 to 8.0 mm for a round stone). Why? It fits perfectly on a standard size 6 or 7 finger. This size provides enough surface area to showcase moissanite's famous "fire" while remaining practical for everyday tasks.

Visualizing Different Carat Ranges

0.5 ct–1.0 cts: Subtle, dainty, and minimalist. It's perfect for those with active lifestyles or a preference for understated elegance.

Pear Cut Moissanite Engagement Ring Infinity Promise Ring Pavé Diamond Ring Rose Gold

1.5–2.5 cts: The classic "statement" look. This size covers about 30-40% of the finger width and commands attention.

Oval Moissanite Engagement Ring Vintage Cluster Promise Wedding Ring in 14K White Gold

Approximately 3.0+ cts: High drama and maximum fire. Best for those who want a "red carpet" look and aren't afraid of the intense rainbow flashes that moissanite produces.

Emerald Cut Moissanite Three Stone Engagement Ring 14K White Gold Bridal Ring for Women

Moissanite vs. Diamond: Carat Size, Appearance, and Visual Performance

Moissanite offers greater brilliance and fire than diamonds, making larger carat sizes appear more vibrant at a fraction of the price. A side-by-side comparison shows what to expect.

Side-by-Side Size Comparison

A 1.0-carat DEW moissanite (6.5 mm) has a virtually identical face-up size and finger coverage to a natural 1.0-carat diamond. This is the advantage of shopping by DEW and millimeters (mm). However, the moissanite will often appear more "lively" due to its higher refractive index.

diamond vs moissanite sparkle and brilliance

Fire, Brilliance, and the "Rainbow Effect"

Moissanite exhibits more fire than diamonds, especially at larger sizes. Due to double refraction, moissanite disperses light more intensely, producing vibrant rainbow flashes.

Stones over 2 carats often show noticeably stronger fire than diamonds, a quality that some buyers love and others prefer more subtle.

Color and Cut Considerations

High-quality D–F color moissanite rivals colorless diamonds in whiteness. Lower-quality stones, however, may show faint yellow or gray tones under strong lighting.

Expert Tip from Juyoyo: Our master cutters optimize the "face-up" surface area of every moissanite. By balancing the depth, we ensure your stone looks its full DEW size without the "fish eye" effect common in poorly cut, mass-produced stones.

Price vs Visual Impact

The value proposition is staggering:

5 ct Natural Diamond: $8,000–$12,000+.
5 ct DEW Moissanite: $400-$600.

Conclusion: Moissanite offers diamond-like size and brilliance at a dramatically lower price, making it one of the best-value gemstones available today.

How to Choose the Right Carat for a Moissanite Engagement Ring

Selecting the perfect carat involves balancing budget, aesthetics, and practicality. Follow this practical guide to narrow your options.

Budget-First Approach: Determine your total ring budget. Allocate 30-40% of your budget for the setting. Then, use our size charts to find the largest millimeter/DEW that fits comfortably within your budget for the gemstone.
Finger Proportions: Petite fingers (sizes 3–5) can make smaller stones (0.5–1.5 ct DEW) look proportionate and elegant. Large fingers (size 7+) can comfortably carry larger stones (2.0+ ctw) without overwhelming the hand.
Setting Choices to Enhance Size: A halo setting of smaller stones around the center stone makes it appear larger. A thin band (1.8–2.0 mm) creates contrast and emphasizes the stone. Shapes like oval, pear, and marquise offer more coverage because they have a greater surface area per carat.

Conclusion

When choosing moissanite, remember this priority: shop by millimeter size first, diamond equivalent weight (DEW) second, and actual carat weight last. Your goal should be to achieve a beautiful visual appearance, which is dictated by the stone’s physical dimensions rather than its weight. Trust your eyes and a millimeter tape measure.

Ready to find your dream ring? Explore Juyoyo’s curated collection of moissanite engagement rings. Or, contact our gemologist for a personalized sizing consultation tailored to your hand, style, and budget.

Moissanite Carat Sizes FAQs

Is a 1-Carat Moissanite the Same as a 1-Carat Diamond?

No, not in weight. A 1-carat moissanite weighs 1 carat, but it will be physically larger than a 1-carat diamond because it is less dense. A moissanite that looks like a 1-carat diamond is described as a 1.00-carat diamond equivalent weight (DEW), which is typically around 6.5 mm for a round cut.

How Many Millimeters Is a 1-Carat Moissanite?

For a round moissanite, one carat of actual carat weight (ACW) is approximately 6.5 mm. However, since the industry uses DEW, you’ll often see stones labeled "1 carat" that are 6.5 mm, which refers to their diamond-equivalent visual size, not their actual weight.

Which Moissanite Shape Looks Largest Per Carat?

Elongated shapes, such as ovals, pears, and marquises, typically appear larger per carat because their surface area is spread out. Among non-elongated shapes, cushion and princess cuts can appear slightly larger than a round stone of the same carat weight due to their different facet patterns and table size.

Do Moissanites Lose Their Sparkle Over Time?

No, because moissanite is a 9.25 on the Mohs hardness scale (diamond is a 10), making it extremely durable and resistant to scratching. Its brilliance and fire are permanent properties of the stone. However, dirt, oils, and lotions can dull the surface, but a simple cleaning will restore its full sparkle instantly.

Does Moissanite Look "Fake" Compared to Diamond?

High-quality, colorless (D–F) moissanite is nearly indistinguishable from a diamond to the naked eye. The main difference is the "fire," or rainbow flashes, which are more intense in moissanite.