Gemstone Size Chart: MM to Carat — Choosing the Perfect Gemstone Wedding Ring
Gemstone Size Chart: MM to Carat — Choosing the Perfect Gemstone Wedding Ring
When shopping for a gemstone wedding ring, one of the most common questions is: “How big will the stone look on my finger?”
Gemstones are measured in millimeters (MM), but often sold by carat weight, and these two numbers don’t always match up the way you think. Understanding the relationship between MM and carat is essential if you want your wedding ring to look exactly how you imagine.
This guide will walk you through the Gemstone Size Chart: MM to Carat, explain why different gemstones have different weights, and help you choose the right size for your dream gemstone wedding ring.
What’s the Difference Between MM and Carat?
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MM (Millimeter): Measures the gemstone’s size (diameter or length × width). This determines how big it will look on your finger.
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Carat: Measures the gemstone’s weight (1 carat = 0.2 grams).
💡 Important: Two gemstones can have the same MM size but very different carat weights because different gems have different densities. For example:
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A diamond and a sapphire of the same size will have slightly different carat weights.
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A quartz gemstone may be lighter than both for the same size.
Gemstone Size Chart (Round Brilliant Cut as Example)
| Diameter (MM) | Approx. Carat Weight |
|---|---|
| 4.0 mm | 0.25 ct |
| 5.0 mm | 0.50 ct |
| 6.5 mm | 1.00 ct |
| 8.0 mm | 2.00 ct |
| 9.0 mm | 2.75 ct |
📌 Note: This chart is based on round brilliant cut stones. Different shapes (oval, pear, cushion, emerald cut) will have slightly different measurements.
Oval-Cut Gemstone Wedding Ring
Here’s a general reference for oval-cut gemstones.
| MM Size | Carat Weight |
| 4x6 mm | ~0.50 ct |
| 5x7 mm | ~1.00 ct |
| 6x8 mm | ~1.50 ct |
| 7x9 mm | ~2.00 ct |
| 8x10 mm | ~3.00ct |
| 9x11 mm | ~4.00 ct |
| 10x12 mm | ~5.00 ct |
| 10x14 mm | ~6.00 ct |
Pear-Shaped Gemstone Wedding Ring
Here’s a general reference for pear-cut gemstones.
| MM Size | Carat Weight |
| 3x5 mm | ~0.15 ct |
| 5x7 mm | ~0.75 ct |
| 6x8 mm | ~1.25 ct |
| 6x9 mm | ~1.50 ct |
| 7x9 mm | ~2.00ct |
| 8x10 mm | ~3.00 ct |
Emerald-Cut Gemstone Wedding Ring
| MM Size | Carat Weight |
| 5x7 mm | ~1.00 ct |
| 6x8 mm | ~2.00 ct |
| 7x9 mm | ~3.00 ct |
| 8x10 mm | ~4.00 ct |
| 10x12 mm | ~6.00ct |
Cushion-Cut Gemstone Wedding Ring
Here’s a general reference for cushion-cut gemstones.
| MM Size | Carat Weight |
| 4 mm | 0.25 ct. – 0.4 ct. |
| 5 mm | 0.32 ct. – 0.8 ct. |
| 6 mm | 0.62 ct. – 1.25 ct. |
| 7 mm | 0.85 ct. – 1.85 ct. |
| 8 mm | 1.25 ct. – 3.23 ct. |
| 9 mm | 1.65 ct. – 4 ct. |
| 10 mm | 2.1 ct. – 5.5 ct. |
Princess-Cut Gemstone Wedding Ring
Here’s a general reference for princess-cut gemstones.
| MM Size | Carat Weight |
| 4 mm | 0.37 ct |
| 5 mm | 0.7 ct. |
| 6 mm | 1.2 ct. |
| 7 mm | 2.0 ct. |
| 8 mm | 3.0 ct. |
| 9 mm | 4.0 ct. |
Heart-Cut Gemstone Wedding Ring
Here’s a general reference for heart-cut gemstones.
| MM Size | Carat Weight |
| 4 mm | 0.14 ct. – 0.32 ct. |
| 5 mm | 0.27 ct. – 0.6 ct. |
| 6 mm | 0.5 ct. – 0.92 ct. |
| 6.5 mm | 1 ct. |
| 7 mm | 0.67 ct. – 1.8 ct. |
| 8 mm | 0.98 ct. – 2.1 ct. |
| 9 mm | 1.35 ct. – 4 ct. |
| 10 mm | 2.52 ct. – 3.7 ct. |
Marquise-Cut Gemstone Wedding Ring
Here’s a general reference for marquise-cut gemstones.
| MM Size | Carat Weight |
| 4×2 mm | 0.07 ct. – 0.12 ct. |
| 5×2.5 mm | 0.11 ct. 0.2 ct. |
| 6×3 mm | 0.17 ct. – 0.32 ct. |
| 7×3.5 mm | 0.35 ct. – 0.45 ct. |
| 8×4 mm | 0.4 ct. – 0.6 ct. |
| 9×4.5 mm | 0.7 ct. – 0.88 ct. |
| 10×5 mm | 0.8 ct. – 1.45 ct. |
| 12×6 mm | 1.3 ct. – 2.15 ct. |
| 13×6.5 mm | 2.2 ct. |
| 14×7 mm | 2.8 ct. |
Kite-Cut Gemstone Wedding Ring
Here’s a general reference for kite-cut gemstones.| Shape-MM Size | Carat Weight |
| 6x9mm | ~1.00 ct |
| 7x10mm | ~1.50 ct |
| 8x11mm | ~2.00 ct |
Hexagon-Cut Gemstone Wedding Ring
Here’s a general reference for hexagon-cut gemstones.| Shape-MM Size | Carat Weight |
| 6mm | ~1.00 ct |
| 7mm | ~1.50 ct |
| 5x9mm | ~1.00 ct |
Why This Matters for a Gemstone Wedding Ring
When choosing your gemstone wedding ring:
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Finger Proportion: A 1.00 ct (6.5 mm) gemstone looks balanced on most hands, but petite fingers may prefer 0.50–0.75 ct.
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Setting Style: Halo or cluster settings can make a smaller gemstone look larger without increasing carat weight.
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Gemstone Type: Some gemstones like opal or moonstone are cut larger for visual impact, while denser stones like sapphire may appear smaller for the same carat weight.
Tips for Choosing the Perfect Size
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Think in MM, not just carats — This ensures you know exactly how the gemstone will look.
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Consider the gemstone type — Density matters!
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Match your lifestyle — Larger stones are eye-catching, but smaller ones may be more comfortable for everyday wear.
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Ask for custom sizing — Many jewelers (including us) can source the perfect size to match your style and comfort.
Our Expertise in Custom Gemstone Wedding Rings
At WillWork Jewelry, we specialize in handcrafted gemstone wedding rings that blend artistry with precision. Whether you dream of a deep-blue sapphire, a romantic pink tourmaline, or a mystical moonstone, we guide you through size selection so your ring looks perfect from every angle.
Conclusion
Understanding the Gemstone Size Chart: MM to Carat empowers you to make confident decisions when choosing your gemstone wedding ring. Remember — the right size is not just about numbers; it’s about how the stone feels, looks, and tells your story.
💍 Ready to find your perfect gemstone wedding ring? Explore our gemstone wedding ring here or contact us to design your own.
