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.

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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!

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.

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.
5×3 mm	0.15 ct. – 0.33 ct.
6×4 mm	0.24 ct. – 0.66 ct.
7×5 mm	0.45 ct. – 1 ct.
8×6 mm	0.8 ct. – 1.55 ct.
9×7 mm	1.1 ct. – 2.76 ct.
10×8 mm	1.45 ct. – 4.21 ct.
11×9 mm	3 ct. – 5.28 ct.
12×10 mm	3.75 ct. – 8.12 ct.

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
4×3 mm	0.25 ct. – 0.3 ct.
5×3 mm	0.25 ct. – 0.44 ct.
6×4 mm	0.45 ct. – 0.7 ct.
7×5 mm	0.75 ct. – 1.2 ct.
8×6 mm	1.15 ct. – 1.95 ct.
9×7 mm	1.8 ct. – 3 ct.
10×8 mm	2.52 ct. – 4 ct.
11×9 mm	3.33 ct. – 5.6 ct.
12×10 mm	4.25 ct. – 7.45 ct.

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
6×4 mm	0.5 ct. – 0.62 ct.
7×5 mm	0.7 ct. – 1.1 ct.
8×6 mm	1.2 ct. – 1.8 ct.
9×7 mm	1.4 ct. – 2.9 ct.
10×8 mm	2.38 ct. – 3.55 ct.
11×9 mm	3.45 ct. – 4.6 ct.
12×10 mm	4 ct. – 6.51 ct.

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.

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
4×3 mm	0.12 ct. – 0.35 ct.
5×4 mm	0.2 ct. – 0.45 ct.
6×4 mm	0.24 ct. – 0.55 ct.
7×5 mm	0.42 ct. – 1 ct.
8×5 mm	0.45 ct. – 1.45 ct.
9×7 mm	0.85 ct. – 1.9 ct.
10×8 mm	1.87 ct. – 3 ct.
12×8 mm	2.23 ct. – 3.8 ct.
14×9 mm	3.6 ct. – 5 ct.

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.

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
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.

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
4×2 mm	0.11 ct.
5×3 mm	0.33 ct.
6×4 mm	0.7 ct.
7×5 mm	1.2 ct.
8×6 mm	1.8 ct.
9×7 mm	2.7 ct.
10×8 mm	3.9 ct.
11×9 mm	5.3 ct.
12×10 mm	7.2 ct.
14×10 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.
5×2.5mm	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 9×7 mm stone size?

A 9×7 mm stone size refers to the stone’s height and width. For this size, different cuts can have different carat weights. For example, a 9×7 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.