Lab Diamond Size Guide

Lab Diamond Shape

In this article, we'll go through everything you need to know about lab diamond sizes.

What is a Lab Diamond Size Chart?

A lab diamond size chart is something that helps you understand the millimeter size of each diamond compared to its carat weight. Carat weight alone usually isn't enough to make a decision on what diamond is best, knowing the millimeter measurements helps you figure out what the best option is depending on your budget.

Each diamond shape will look different depending on its carat weight. Even when lab diamonds are different sizes, their carat weight can still remain the same.

Why is a Diamond's Millimeter Measurement Important?

Knowing a lab diamond's millimeter measurement is important because it lets you know the true size of it. There are other instances when it can help too, such as when you're buying a diamond for a ring setting that already exists. It normally needs the exact millimeter size of the lab diamond to make sure it will fit.

A diamond's millimeter measurement is also important when it comes to diamond shapes that aren't round, such as emerald and cushion lab diamonds. When you purchase high-quality lab diamonds, you will always be able to know both the millimeter measurements and carat weight of it.

What are “Pointers”?

Pointers is a term regularly used in trade and wholesale. It refers to the diamond millimeter size and carat weight. When the lab diamonds weight under one carat, they can be referred to as pointers. For example, a one-pointer is a 0.01 carat diamond. A two-pointer is a 0.2 carat diamond, and twenty-five pointer diamond refers to a 0.25 carat diamond.

Type of Lab Diamond Shapes


Round lab diamonds are the most classic and popular diamond shape. They are most often used for engagement rings. Round diamonds have the most brilliance and maximum sparkle. From the top view, round diamonds appear larger than princess diamonds, emerald, cushion, asscher and radiant diamonds. At the same time, they appear smaller from the top than oval, pear, and marquise diamonds.

MM Size Carat Weight MM Size Carat Weight
0.8 mm 0.0025 ct 7 mm 1.30 ct
1 mm 0.005 ct 7.3 mm 1.50 ct
1.15 mm 0.0067 ct 7.5 mm 1.67 ct
1.12 mm 0.0075 ct 7.75 mm 1.75 ct
1.25 mm 0.01 ct 8 mm 2.00 ct
1.3 mm 0.01 ct 8.25 mm 2.11 ct
1.5 mm 0.015 ct 8.5 mm 2.43 ct
1.75 mm 0.02 ct 8.7 mm 2.50 ct
1.8 mm 0.025 ct 9 mm 2.75 ct
2 mm 0.03 ct 9.1 mm 3.00 ct
2.25 mm 0.04 ct 9.5 mm 3.35 ct
2.5 mm 0.06 ct 9.75 mm 3.61 ct
2.75 mm 0.08 ct 10 mm 3.87 ct
3 mm 0.11 ct 10.25 mm 4.16 ct
3.25 mm 0.14 ct 10.5 mm 4.41 ct
3.5 mm 0.17 ct 10.75 mm 4.57 ct
3.75 mm 0.21 ct 11 mm 4.91 ct
4 mm 0.25 ct 11.25 mm 5.49 ct
4.25 mm 0.28 ct 11.5 mm 5.85 ct
4.5 mm 0.36 ct 12 mm 6.84 ct
4.75 mm 0.44 ct 12.25 mm 7.26 ct
5 mm 0.50 ct 12.5 mm 7.36 ct
5.25 mm 0.56 ct 12.75 mm 7.52 ct
5.5 mm 0.66 ct 13 mm 8.51 ct
5.75 mm 0.75 ct 13.5 mm 9.53 ct
6 mm 0.84 ct 14 mm 10.49 ct
6.25 mm 0.93 ct 15 mm 12.89 ct
6.5 mm 1.00 ct 16 mm 16.06 ct
6.8 mm 1.25 ct 17 mm 18.00 ct


Emerald cut lab diamonds are rectangular in shape with trimmed corners. They provide a sophisticated look with elegance. Their design was developed in the 1500s. Since emerald cut diamonds have flat parallel facets, they produce an effect referred to as “hall of mirrors”. These diamonds aren’t as brilliant as round diamonds, they offer a more clean look with clarity and lustre. They are right in the middle when it comes to diamond size, similar to radiant diamonds. Due to their rectangular size, they sometimes give the illusion of appearing larger than they actually are.

MM Size Carat Weight MM Size Carat Weight
3x2 mm 0.10 ct 9x7 mm 2.50 ct
3.5x2 mm 0.12 ct 10x7.5 mm 3.00 ct
4x2 mm 0.15 ct 9.5x7.5 mm 3.21 ct
4x3 mm 0.20 ct 10x8 mm 3.79 ct
5x3 mm 0.29 ct 11x9 mm 5.21 ct
5.5x3.5 mm 0.46 ct 12x8 mm 5.34 ct
6x4 mm 0.50 ct 12x10 mm 6.00 ct
6.5x4 mm 0.75 ct ct 14x8 mm 6.25 ct
6.5x4.5 mm 0.88 ct 13x9 mm 6.38 ct
7x5 mm 1.00 ct 14x10 mm 8.48 ct
7.3x5.3 mm 1.25 ct 13x11 mm 9.13 ct
7.5x5.5 mm 1.50 ct 14x12 mm 11.26 ct
8x6 mm 1.75 ct 16x12 mm 14.22 ct
8.5x6.5 mm 2.00 ct 17x13 mm 16.50 ct


Cushion cut lab diamonds are either square or rectangular in shape. They have rounded corners, sometimes resembling the shape of pillow. This is why they are sometimes called pillow cuts, along with candlelight cuts. They are fiery, but not as brilliant as round diamonds. They have a romantic appeal to them. Cushion diamonds usually look smaller than other diamond shapes, even of similar weight.

MM Size Carat Weight
4.2 mm 0.40 ct
4.9 mm 0.50 ct
5.25 mm 0.75 ct
5.5 mm 1.00 ct
6 mm 1.25 ct
6.5 mm 1.50 ct
7 mm 2.00 ct
7.5 mm 2.50 ct
8 mm 3.00 ct
8.5 mm 3.5 ct
9 mm 4.12 ct
9.5 mm 5.09 ct
10 mm 5.62 ct
11 mm 7.44 ct
12 mm 9.52 ct
13 mm 12.66 ct


A princess cut lab diamond has great brilliance along with sparkle. They are a classic, with a contemporary look. They are the second most popular choice for engagement rings, after the round diamond. They are the most popular of all the fancy shapes though. The princess cut is very modern, it was created in the 1960s. It has a square outline, with a 1:1 ratio of length-to-width. Sometimes they are slightly rectangular depending on the ratio.

MM Size Carat Weight
1.5 mm 0.015 ct
1.75 mm 0.03 ct
2 mm 0.06 ct
2.25 mm 0.08 ct
2.50 mm 0.10 ct
2.75 mm 0.13 ct
3 mm 0.18 ct
3.25 mm 0.26 ct
3.50 mm 0.29 ct
3.75 mm 0.31 ct
4 mm 0.39 ct
4.25 mm 0.44 ct
4.50 mm 0.50 ct
4.75 mm 0.64 ct
5 mm 0.75 ct
5.25 mm 0.75 ct
5.50 mm 1.00 ct
5.75 mm 1.11 ct
6 mm 1.25 ct
6.25 mm 1.39 ct
6.5 mm 1.50 ct
6.75 mm 1.75 ct
7 mm 2.00 ct


An oval lab diamond cut is oval in shape. It's similar to the cushion cut, and very brilliant and fiery. It’s a great alternative if you want something similar to a round diamond, but a bit different in size. When viewed from the top, oval diamonds usually look larger compared to other diamond cuts.

MM Size Carat Weight MM Size Carat Weight
4.5x3.5 mm 0.21 ct 10x8 mm 2.50 ct
5x3 mm 0.21 ct 10.5x8.5 mm 2.88 ct
5.5x3.5 mm 0.33 ct 12x8 mm 3.00 ct
5x4 mm 0.35 ct 11x9 mm 3.85 ct
6x4 mm 0.50 ct 12x10 mm 5.05 ct
6x5 mm 0.61 ct 14x10 mm 5.81 ct
6.5x4.5 mm 0.65 ct 13x11 mm 6.05 ct
7x5 mm 0.75 ct 14x12 mm 8.21 ct
7.7x5.7 mm 1.00 ct 15x12 mm 8.76 ct
8x6 mm 1.25 ct 16x12 mm 9.32 ct
9x6 mm 1.41 ct 16x14 mm 11.88 ct
8.5x6.5 mm 1.50 ct 18x13 mm 12.86 ct
9x7 mm 2.00 ct 20x15 mm 14.96 ct


A marquise lab diamond is elliptical in shape. It’s a brilliant cut, and has narrow points at each end. Marquise diamonds have lots of sparkle. When looking from above, it typically appears bigger than any other diamond shapes of similar carat weight.

MM Size Carat Weight MM Size Carat Weight
3x1.5 mm 0.025 ct 9.5x2 mm 0.85 ct
3.5x1.75 mm 0.065 ct 10.5 mm 1.00 ct
3.5x2 mm 0.07 ct 11x5.5 mm 1.25 ct
4x2 mm 0.10 ct 11.5x6 mm 1.33 ct
3.75x1.75 mm 0.11 ct 12x6 mm 1.50 ct
4.25x2.25 mm 0.12 ct 13x6.5 mm 2.00 ct
5x2.5 mm 0.14 ct 14x7 mm 2.50 ct
5.5x2.75 mm 0.16 ct 15x7 mm 3.00 ct
5.5x3 mm 0.18 ct 14x8 mm 3.00 ct
5x3 mm 0.20 ct 15x7.5 mm 3.25 ct
6.5x3 mm 0.23 ct 15x8 mm 3.44 ct
6x3 mm 0.25 ct 16x8 mm 3.86 ct
7x3 mm 0.30 ct 16.5x8.25 mm 4.00 ct
7.5x3.5 mm 0.33 ct 17x8.5 mm 4.88 ct
7x4 mm 0.34 ct 17.5x10 mm 5.50 ct
8x4 mm 0.50 ct 20x8 mm 7.08 ct
8.75x4.25 mm 0.70 ct 20x10 mm 7.94 ct
9x4.5 mm 0.75 ct 20x11 mm 9.50 ct


Pear cut lab diamonds are a variation of a round cut. It has a pointed end at the top, and is round at the bottom. The pear diamond shape works well for rings, but also pendants and earrings. They are very feminine and brilliant. When viewed from the top, pear cuts usually look larger than most diamond shapes of the same carat weight.

MM Size Carat Weight MM Size Carat Weight
3x2 mm 0.13 ct 12x8 mm 3.00 ct
4x2.5 mm 0.18 ct 12x7 mm 3.12 ct
4x3 mm 0.21 ct 12x9 mm 3.44 ct
5x3 mm 0.25 ct 14x8 mm 3.47 ct
5x4 mm 0.35 ct 13x9 mm 4.11 ct
6x4 mm 0.50 ct 14x9 mm 4.25 ct
6.5x4.5 mm 0.60 ct 15x9 mm 5.06 ct
7x5 mm 0.75 ct 14x10 mm 5.41 ct
7.5x5.5 mm 0.85 ct 13x11 mm 5.65 ct
7.7x5.7 mm 1.00 ct 15x10 mm 5.75 ct
8x6 mm 1.25 ct 16x9 mm 5.86 ct
8.5x6.5 mm 1.50 ct 16x10 mm 6.27 ct
10x6 mm 1.71 ct 16x10 mm 6.46 ct
8.7x6.7 mm 1.80 ct 15x11 mm 7.36 ct
9x7 mm 2.00 ct 18x11 mm 8.14 ct
10x8 mm 2.50 ct 16x12 mm 8.99 ct
11x7.50 mm 2.61 ct 18x12 mm 9.35 ct
13x8 mm 2.98 ct 18x13 mm 10.21 ct
11x8 mm 3.00 ct 19x14 mm 11.70 ct


Asscher lab diamond cuts are similar to emerald cuts. They are a square shape with deep corners. Their shape sometimes seems octagonal, appearing sophisticated and large. When viewed from the top, asscher cuts look the same in size to other diamond shapes of similar weight.

MM Size Carat Weight MM Size Carat Weight
4 mm 0.39 ct 8 mm 3.00 ct
4.5 mm 0.50 ct 8.5 mm 3.50 ct
5 mm 0.75 ct 9 mm 4.12 ct
5.5 mm 1.00 ct 9.5 mm 5.09 ct
6 mm 1.25 ct 10 mm 5.62 ct
6.5 mm 1.50 ct 11 mm 7.44 ct
7 mm 2.00 ct 12 mm 9.52 ct
7.5 mm 2.50 ct 13 mm 12.66 ct


Radiant lab diamonds have the sparkle and brilliance of the round diamond, with a similar elegant look of the emerald diamond. It’s perfect for any type of jewelry, especially engagement rings. This diamond cut has trimmed corners, and a slight rectangular shape.

MM Size Carat Weight MM Size Carat Weight
5x3 mm 0.31 ct 10x8 mm 3.50 ct
4.5x3.5 mm 0.34 ct 11x9 mm 5.05 ct
6x3 mm 0.41 ct 12x9 mm 6.06 ct
6x4 mm 0.50 ct 11.5x10 mm 6.45 ct
6.5x4.5 mm 0.75ct 13x9 mm 6.54 ct
7x5 mm 1.00 ct 12x10 mm 6.79 ct
7.3x5.5 mm 1.25 ct 14x10 mm 8.47 ct
7.5x5.8 mm 1.50 ct 13x11 mm 9.33 ct
8x6 mm 2.00 ct 13.5x11.5 mm 10.19 ct
8.5x6.5 mm 2.25 ct 15x11 mm 11.48 ct
9x7 mm 2.50 ct 14x12 mm 12.14 ct
9.5x7.5 mm 3.00 ct 16x12 mm 14.22 ct
10x7 mm 3.31 ct 17x13 mm 16.22 ct


What Size Diamond is Good for a Necklace?

The size of diamond that would be good for a necklace depends on your personal preference and budget. Do you want a small diamond or a larger one? Larger diamonds anywhere from 1 - 1.5 carat might be too much for everyday wear, whereas smaller sizes such as 0.5 carat is perfect for an every day outfit.

Is Carat Weight the Same as Diamond's Size?

Carat weight is not the same as diamond size. Carat actually measures the weight of the diamond, rather than the size. For example, 1 carat is 0.2 grams. Despite the correlation between the two, the carat weight doesn’t reveal the size of the diamond. This is where labs can be useful.

What is the best diamond size for your engagement ring?

On average, a diamond center stone of 1.0 carat seems to be the most popular engagement ring size. Going smaller or bigger depends on personal preference, style and budget. Lately, we have seen a shift towards larger diamonds between 1.25 carats and 1.50 carats.
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