Colored Gemstone Size Chart: MM to Carat
When shopping for gemstone jewelry, the three big gemstones—emerald, sapphire, and ruby—are typically the go-to options. These alluring, precious gemstones are set apart by their unique qualities like their vibrant colors, durability and varying weights. In this guide, we’ll help you understand why gemstone weight is important in discovering the true value of a stone. We’ll also provide you with gemstone mm to carat conversions to help you get the specific stone size when you shop for gemstone earrings, bracelets, rings and more.
Explore ruby, emerald & sapphire jewelry that matches your style. MM to Carat guide ahead helps you choose the right gemstone size with ease.
Millimeter vs. Carat: Understanding the Difference
The millimeter measurement of a gemstone refers to its diameter, which provides an accurate gauge of the stone’s size when viewed from the top. The gemstone mm dimensions can vary depending on the type of stone, carat weight and cut. This is different from carat which measures the weight of the gemstone. The actual gemstone carat size can vary due to factors like the stone’s shape, cut, facets and density. Unlike carat weight, millimeters offer a more accurate way to measure a gemstone’s size.
Why Do Gemstones Have Different Weights?
Generally, most gemstones have different weights because they are made of different minerals. For example, ruby and sapphire are made of corundum, while emeralds are made of beryl. These minerals have different densities which affect the weight of a gemstone. Although ruby and sapphire are part of the same mineral family, the size of a one-carat ruby can still differ from that of a one-carat sapphire because the gemstone’s cut is another factor that affects its overall weight and size.
For instance, a 9x7mm emerald-cut ruby has a carat weight of 3, while an emerald and blue sapphire of the same cut and dimension will have carat weights of 2.25 and 2.45, respectively. This is why we’ve created a gemstone carat weight chart to make the conversion to millimeters easy for you.
What are Pointers?
Pointers are a unique method of measuring the weight of small diamonds. To grasp the concept of pointers, it's essential to understand carats first.
A carat is a unit of measurement for gemstones and is equivalent to 200 milligrams. To measure a stone precisely, one carat has been further divided into 100 points down to the hundredth decimal place. For example, a 0.36-carat stone can be referred to as a ‘thirty-six pointer’ and a 2.10-carat stone as ‘two point one zero carats.’ Basically, pointers provide an accurate method for measuring the weight of small diamonds.
Carat weight significantly influences the overall price of a gemstone. Generally, a higher carat weight translates to a more expensive gemstone. If you’re looking for a larger carat size without the hefty price tag, lab-grown gemstones are an excellent option. These gemstones are chemically, physically and optically identical to natural gemstones but are up to 90% less expensive.
With pointers and carat weight in mind, let’s explore how different gemstone shapes and cuts impact size and weight. Check out our handy conversion guide for gemstones below to see how these factors play out in your favorite cuts!
Read: Natural vs. Lab-Grown Gemstones
Round Gemstones
The round brilliant cut is the most popular, especially when it comes to gemstone rings for women. It has 57 facets that make the stone sparkle brilliantly whenever it catches the light. This is the gemstone mm to carat calculator you need for brilliant round gemstones.
| Round MM Size | Round Carat Weight |
| 4 mm | 0.16 ct. - 0.34 ct. |
| 5 mm | 0.32 ct. - 0.7 ct. |
| 6 mm | 0.5 ct. - 1.14 ct. |
| 7 mm | 0.75 ct. - 1.6 ct. |
| 8 mm | 1.15 ct. - 2.65 ct. |
| 9 mm | 1.5 ct. - 3.75 ct. |
| 10 mm | 1.9 ct. - 5 ct. |
- Shared Prong Sapphire and Diamond Half Eternity Ring$8,180 $9,089
- Round Blue Sapphire Stud Earrings$34,424 $38,249
- Classic Prong-Set Round Blue Sapphire Solitaire Pendant$22,769 $25,299
- Classic Round Sapphire and Diamond Tennis Bracelet$19,286 $21,429
- Shared Prong Emerald and Diamond Half Eternity Ring$5,093 $5,659
- Round Emerald Stud Earrings$67,031 $74,479
- Classic Prong-Set Round Emerald Solitaire Pendant$29,744 $33,049
- Classic Round Emerald and Diamond Tennis Bracelet$27,431 $30,479
- Half Eternity Seven Stone Ruby and Diamond Wedding Ring$4,940 $5,489
- Round Ruby Stud Earrings$148,679 $165,199
- Classic Prong-Set Round Ruby Solitaire Pendant$61,604 $68,449
- Prong-Set Round Ruby Link Tennis Bracelet$7,739 $8,599
Oval-Cut Gemstones
The oval cut is known to resemble the traditional round brilliant cut, but it is slightly elongated, creating an illusion of a larger stone. With 58 facets, oval-cut gemstones sparkle beautifully. When choosing the right carat weight, use this gemstone carat weight calculator to determine its actual size.
| Oval MM Size | Oval Carat Weight |
| 4x3mm | 0.12 ct. - 0.28 ct. |
| 5x3 mm | 0.15 ct. - 0.33 ct. |
| 6x4 mm | 0.24 ct. - 0.66 ct. |
| 7×5 mm | 0.45 ct. - 1 ct. |
| 8x6 mm | 0.8 ct. - 1.55 ct. |
| 9x7 mm | 1.1 ct. - 2.76 ct. |
| 10x8 mm | 1.45 ct. - 4.21 ct. |
| 11x9 mm | 3 ct. - 5.28 ct. |
| 12x10 mm | 3.75 ct. - 8.12 ct. |
- Five Stone Blue Sapphire and Diamond Wedding Ring$4,760 $5,289
- Basket-Set Oval Blue Sapphire Stud Earrings with Diamond$13,787 $15,319
- Shell Style Oval Sapphire and Diamond Pendant$7,577 $8,419
- Classic Oval Blue Sapphire and Diamond Tennis Bracelet$15,497 $17,219
- Oval Emerald Side Stone Engagement Ring with Diamonds$10,718 $11,909
- Oval Emerald Leverback Drop Earrings$15,533 $17,259
- Vintage Style Emerald Pendant with Diamond Halo$9,053 $10,059
- Classic Oval Emerald and Diamond Tennis Bracelet$24,785 $27,539
- Five Stone Ruby and Diamond Wedding Ring$4,976 $5,529
- Prong-Set Solitaire Oval Ruby Stud Earrings$21,014 $23,349
- Shell Style Oval Ruby and Diamond Pendant$10,943 $12,159
- Alternating Oval Ruby and Round Diamond Tennis Bracelet$9,260 $10,289
Emerald-Cut Gemstones
An emerald-cut gemstone is rectangular in shape with rounded corners and elongated parallels. With its 57 facets, it offers incredible brilliance and sparkle, quite similar to a round brilliant or cushion cut. This is the actual gemstone size chart for an emerald-cut gemstone.
| Emerald MM Size | Emerald Carat Weight |
| 4x3 mm | 0.25 ct. - 0.3 ct. |
| 5x3 mm | 0.25 ct. - 0.44 ct. |
| 6x4 mm | 0.45 ct. - 0.7 ct. |
| 7×5 mm | 0.75 ct. - 1.2 ct. |
| 8x6 mm | 1.15 ct. - 1.95 ct. |
| 9x7 mm | 1.8 ct. - 3 ct. |
| 10×8 mm | 2.52 ct. - 4 ct. |
| 11x9 mm | 3.33 ct. - 5.6 ct. |
| 12x10 mm | 4.25 ct. - 7.45 ct. |
- Emerald-Cut Blue Sapphire Criss Cross Solitaire Engagement Ring$4,094 $4,549
- Emerald-Cut Sapphire Stud Earrings with Diamond Halo$17,531 $19,479
- GIA Certified Octagonal Blue Sapphire Horseshoe Halo Pendant$25,919 $28,799
- GIA Certified Emerald-Cut Emerald Halo Ring with Diamonds$20,069 $22,299
- Emerald-Cut Emerald Stud Earrings with Diamond Halo$33,254 $36,949
- Emerald-Cut Emerald Halo Pendant$17,198 $19,109
- Emerald & Diamond Multi-Shape Tennis Bracelet$36,278 $40,309
- Emerald-Cut Ruby Halo Knife-Edge Shank Engagement Ring$26,540 $29,489
- Emerald-Cut Ruby Solitaire Leverback Earrings$49,670 $55,189
- Emerald-Cut Ruby Pendant with Diamond Trio$25,748 $28,609
- Horizontally Set Emerald-Cut Ruby Bolo Bracelet$30,149 $33,499
Cushion-Cut Gemstones
A cushion cut can be rectangular or square with rounded edges resembling a pillow. Its 58 facets give gemstones their alluring brilliance. You can make use of this gemstone carat size chart to find the true size of the cushion-cut gemstone you’re looking for.
| Cushion Rectangular MM Size | Cushion Rectangular Carat Weight |
| 6x4 mm | 0.5 ct. - 0.62 ct. |
| 7x5 mm | 0.7 ct. - 1.1 ct. |
| 8x6 mm | 1.2 ct. - 1.8 ct. |
| 9x7 mm | 1.4 ct. - 2.9 ct. |
| 10x8 mm | 2.38 ct. - 3.55 ct. |
| 11x9 mm | 3.45 ct. - 4.6 ct. |
| 12x10 mm | 4 ct. - 6.51 ct. |
- Rectangular Cushion Sapphire Infinity Pendant$4,823 $5,359
| Cushion Square MM Size | Cushion Square 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. |
- Vintage Style Cushion Sapphire Solitaire Engagement Ring$35,468 $39,409
- Cushion Sapphire Pendant with Diamond Halo$3,491 $3,879
- Bezel-Set Cushion Blue Sapphire Tennis Bracelet with Diamond Accents$11,861 $13,179
- Vintage Style Cushion Emerald Solitaire Engagement Ring$35,387 $39,319
- Cushion Emerald Studs with Diamond Halo$2,852 $3,169
- Infinity Twist Emerald Pendant with Diamond Accents$2,204 $2,449
Pear-Cut Gemstones
Pear shape, also referred to as modified brilliant cut, is a blend of two different cuts—an oval cut with one rounded end and a marquise cut with one pointed end. They have 57 facets, offering a brilliance similar to that of a round brilliant stone, but they appear bigger in comparison.
| Pear MM Size | Pear Carat Weight |
| 4x3 mm | 0.12 ct. - 0.35 ct. |
| 5x4 mm | 0.2 ct. - 0.45 ct. |
| 6x4 mm | 0.24 ct. - 0.55 ct. |
| 7x5 mm | 0.42 ct. - 1 ct. |
| 8x5 mm | 0.45 ct. - 1.45 ct. |
| 9x7 mm | 0.85 ct. - 1.9 ct. |
| 10x8 mm | 1.87 ct. - 3 ct. |
| 12x8 mm | 2.23 ct. - 3.8 ct. |
| 14x9 mm | 3.6 ct. - 5 ct. |
- Bypass Pear-Shaped Blue Sapphire Ring$2,087 $2,319
- Pear Emerald Solitaire Engagement Ring with Trio Diamond Accents$5,102 $5,669
- Prong-Set Emerald Teardrop V-Bale Pendant with Diamond$5,822 $6,469
- Pear and Marquise Emerald Olive Branch Bracelet$1,844 $2,049
- Prong-Set Ruby Teardrop V-Bale Pendant with Diamond$9,458 $10,509
- Pear and Marquise Ruby Olive Branch Bracelet$1,637 $1,819
Princess-Cut Gemstones
A princess-cut is a square or rectangular stone with 57 facets and sharp corners. It is a popular choice for engagement rings and is often referred to as a modern alternative to a round brilliant cut. Use this mm to carat gemstone weight calculator to find out the true size of a princess-cut stone.
| Princess MM Size | Princess Carat Weight |
| 4 mm | 0.37 ct |
| 5 mm | 0.7 ct. |
| 6 mm | 1.2 ct. |
| 7 mm | 1.8 ct. |
| 8 mm | 2.8 ct. |
| 9 mm | 3.9 ct. |
Heart-Cut Gemstones
A heart-cut stone is one of the most popular fancy shapes. With its 57 triangular and kite-shaped facets, it enhances the brilliance and fire of a stone making it sparkle as much as a round or princess cut. Use this mm to carat conversion for gemstones to discover the size of a heart-cut gemstone.
| Heart MM Size | Heart 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. |
- Solitaire Sapphire Heart Promise Ring with Diamond Accents$1,718 $1,909
- Heart-Shaped Blue Sapphire and Diamond Swirl Drop Earrings$1,484 $1,649
- Heart-Shaped Blue Sapphire Infinity Pendant with Diamond Accents$3,527 $3,919
- Solitaire Emerald Heart Engagement Ring with Diamond Accents$5,354 $5,949
- Emerald Solitaire Heart Stud Earrings$3,131 $3,479
- Heart-Shaped Emerald Rabbit Ear Bale Pendant$7,874 $8,749
- Heart-Shaped Emerald Infinity Bolo Bracelet$3,923 $4,359
- Solitaire Heart Ruby and Diamond Chevron Ring$2,501 $2,779
- Heart-Shaped Ruby and Diamond Swirl Drop Earrings$1,529 $1,699
- Heart-Shaped Ruby Rabbit Ear Bale Pendant$11,339 $12,599
- Heart-Shaped Ruby Infinity Bolo Bracelet$6,353 $7,059
Marquise-Cut Gemstones
Marquise-cut gemstones have an elongated elliptical shape with signature pointed ends. Their long, narrow shape makes the stone appear bigger, and its 58 facets give the stone a captivating sparkle. Use the chart below to easily get your conversions.
| Marquise MM Size | Marquise Carat Weight |
| 4x2 mm | 0.07 ct. - 0.12 ct. |
| 5x2.5 mm | 0.11 ct. 0.2 ct. |
| 6x3 mm | 0.17 ct. - 0.32 ct. |
| 7x3.5 mm | 0.35 ct. - 0.45 ct. |
| 8x4 mm | 0.4 ct. - 0.6 ct. |
| 9×4.5 mm | 0.7 ct. - 0.88 ct. |
| 10x5 mm | 0.8 ct. - 1.45 ct. |
| 12x6 mm | 1.3 ct. - 2.15 ct. |
| 13×6.5 mm | 2.2 ct. |
| 14x7 mm | 2.8 ct. |
- Marquise Sapphire Olive Leaf Ring$2,384 $2,649
- Marquise and Round Blue Sapphire Cross Pendant$1,835 $2,039
- East-West Marquise Sapphire Bolo Bracelet with Halo$1,079 $1,199
- Emerald and Diamond Butterfly Bypass Ring$3,599 $3,999
- Marquise and Round Emerald Cross Pendant$2,501 $2,779
- East-West Marquise Emerald Bolo Bracelet with Halo$1,052 $1,169
- Tilted Marquise Ruby Solitaire Parallel Split Shank Engagement Ring$1,160 $1,289
- Marquise Ruby Olive Branch Pendant$2,132 $2,369
- East-West Marquise Ruby Bolo Bracelet with Halo$1,034 $1,149
Radiant-Cut Gemstones
Radiant-cut is part of the step-cut family and is mostly rectangular-shaped but can also be square. With 70 facets, it gives a stone an eye-catching brilliance and appearance. Use the conversion chart to determine the actual size of a radiant cut gemstone.
| Radiant MM Size | Radiant Carat Weight |
| 4x2 mm | 0.11 ct. |
| 5x3 mm | 0.33 ct. |
| 6x4 mm | 0.7 ct. |
| 7x5 mm | 1.2 ct. |
| 8x6 mm | 1.8 ct. |
| 9x7 mm | 2.7 ct. |
| 10x8 mm | 3.9 ct. |
| 11x9 mm | 5.3 ct. |
| 12x10 mm | 7.2 ct. |
| 14x10 mm | 9.3 ct. |
Baguette-Cut Gemstones
A baguette is long, rectangular, and thin, featuring 14 facets and pointed corners. It is frequently used as a side or accent stone to enhance the sparkle of the center stone, which is why it is usually found in smaller carat weights. However, that doesn’t make it a less desirable option for a center stone.
| Baguette MM Size | Baguette Carat Weight |
| 4x2mm | 0.06 ct. |
| 5x2.5mm | 0.2 ct. |
| 6x2mm | 0.18 ct. |
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Frequently Asked Questions
Q1. What is carat in gemstones
A carat is a unit of weight used to measure gemstones, with one carat equaling 200 milligrams. It helps determine the size and value of your gemstone.
Q2. How to determine the carat size of gemstones
Carat size is based on a gemstone’s measurements, like its depth, height, and width. Since different gemstones have varying densities and cuts, carat sizes can differ even for stones of the same dimensions. To figure out the carat size, you’ll often measure the diameter and consider the stone’s shape and density.
Q3. What is a 9x7 mm stone size?
A 9x7 mm stone size refers to the stone’s height and width. For this size, different cuts can have different carat weights. For example, a 9x7 mm radiant cut might weigh around 2.7 ct., while the same size in an emerald cut ranges from 1.8 ct. to 3 ct., and in a pear cut, it could be between 0.85 ct. and 1.9 ct.
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