Mm to Carat Weight Conversions for Diamonds Guide

Diamonds are measured using units called "carats," but many are unaware that carats are measures of weight rather than dimensions.
Carat weight impacts how your diamond looks, but it does not directly equate to size. As a matter of fact, two diamonds of the same weight can appear very differently depending on how they carry the weight.
Simon G. MR1394 Fabled Diamond Engagement Ring
Simon G. MR1394 Fabled Diamond Engagement Ring
As well as affecting the appearance of a diamond, poor cutting can keep additional weight "hidden" under its girdle - the base of the diamond that is typically covered by the ring. For example, poorly cut 1.25 ct. round diamonds can appear the same size to the naked eye as well cut 1 ct. round diamonds.
Elongated fancy-shaped diamonds with shallower depths and longer dimensions can take up more real estate on a finger or in a ring than classic round diamonds.
Carat weight is only an indicator of how large or small a diamond will appear. That’s why all diamonds at Whiteflash are listed with detailed specifications including weight, measurement, cut quality, and imaging to ensure you get the best value for your money.
Here are the approximate millimeter (mm) to carat weight conversions for well-cut round cut diamonds and princess cut diamonds for reference.
  • Mm To Carat Conversion Chart: Round Cut Diamonds
  • Mm To Carat Conversion Chart: Princess Cut Diamonds
  • Most Popular Engagement Ring Diamond Carat
Diamond Carat to Millimeter Chart

MM To Carat Conversion Chart: Round Cut Diamonds

There is no doubt that round cut diamonds remain the most popular choice for fine jewelry.
The illustrious round cut diamond has a long and rich history, with diamond cutters and experts studying its light performance for decades and refining precise equations to enhance its brilliance, scintillation, and fire over time.
Due to its spectacular brilliance and beauty, this shape is by far the most classic and popular choice.
A round brilliant diamond has approximately the same diameter all the way around, as any circle.
The stone's diameter is determined by an imaginary line connecting two points across from each other on the stone's girdle, which is seen when looking at the stone from the top.
Round MM Size
Round Carat Weight
 
0.8 mm
0.0025 ct
1 mm
0.005 ct
1.1 mm
0.0067 ct
1.2 mm
0.009 ct
1.25 mm
0.01 ct
1.5 mm
0.015 ct
1.75 mm
0.02 ct
1.8 mm
0.025 ct
2 mm
0.03 ct
2.2 mm
0.04 ct
2.5 mm
0.06 ct
2.75 mm
0.08 ct
3 mm
0.10 ct
3.25 mm
0.14 ct
3.5 mm
0.17 ct
3.75 mm
0.21 ct
4 mm
0.25 ct
4.25 mm
0.28 ct
4.5 mm
0.36 ct
4.75 mm
0.44 ct
5 mm
5.25 mm
0.56 ct
5.5 mm
0.66 ct
5.75 mm
6 mm
0.84 ct
6.25 mm
0.93 ct
6.5 mm
6.8 mm
1.25 ct
7 mm
1.30 ct
7.3 mm
7.5 mm
1.67 ct
7.75 mm
1.75 ct
8 mm
8.25 mm
2.11 ct
8.5 mm
2.43 ct
8.7 mm
2.50 ct
9 mm
2.75 ct
9.1 mm
9.5 mm
3.35 ct
9.75 mm
3.61 ct
10 mm
3.87 ct
10.25 mm
10.5 mm
4.41 ct
10.75 mm
4.57 ct
11 mm
11.25 mm
5.49 ct
11.5 mm
5.85 ct
12 mm
6.84 ct
12.25 mm
7.26 ct
12.5 mm
7.36 ct
12.75 mm
7.52 ct
13 mm
8.51 ct
13.5 mm
9.53 ct
14 mm

MM To Carat Conversion Chart: Princess Cut Diamonds

The princess cut diamond seamlessly blends classic diamond sparkle with a contemporary silhouette, resulting in a diamond that has both a modern look and classic performance. First introduced in the 1960s, it is relatively new to the diamond shape menu.
In terms of popularity, the princess cut is second only to the round cut, offering brilliance, scintillation and something truly different to brides.
Princess cut diamonds encompass a group of similar faceting patterns that are described as square or rectangular modified brilliant cuts.
Princess carat weights can be somewhat misleading as to visual size when compared to rounds, based on the dimensions used to communicate them. An understanding of a round's footprint or "spread" is largely dependent on its depth percentage, which is determined by its depth, diameter, and girdle thickness.
Using the smallest width to total depth ratio, we calculate the dimensions and depth percentage of a princess cut diamond, resulting in relatively greater depth and smaller dimension. It’s important to realize this method of calculation exaggerates the impression many people have that princess cuts look smaller than rounds carat for carat.
Princess MM Size
Princess 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
2.5 mm
0.10 ct
2.75 mm
0.13 ct
3 mm
0.18 ct
3.25 mm
0.26 ct
3.5 mm
0.29 ct
3.75 mm
0.31 ct
4 mm
0.39 ct
4.25 mm
0.44 ct
4.5 mm
4.75 mm
0.64 ct
5 mm
5.25 mm
0.90 ct
5.5 mm
5.75 mm
1.11 ct
6 mm
1.25 ct
6.25 mm
1.39 ct
6.5 mm
6.75 mm
1.75 ct
7 mm
7.25 mm
2.01 ct
7.5 mm
2.50 ct
7.75 mm
2.74 ct
8 mm
8.25 mm
3.24 ct
8.5 mm
3.67 ct
8.75 mm
9 mm
4.12 ct
9.5 mm
9.75 mm
5.36 ct
10 mm
5.62 ct
10.25 mm
5.76 ct
10.5 mm
5.99 ct
11 mm
7.44 ct
11.5 mm
9.44 ct
12 mm
While a well-made 1ct carat round cut diamond is approximately 6.5mm in diameter and a 1ct princess cut diamond around 5.5mm, the princess has extended surface area out to the corners.
In terms of aesthetics and flavor - it's certainly different - but the disparity in size is not as big as it appears on paper due to the math used in the calculations.
A CUT ABOVE® is the most carefully crafted, comprehensively analyzed and thoroughly reviewed diamond in the world. It starts with the selection of high-quality rough diamond crystals, and world-class skill and attention to detail by master cutters working with state-of-the-art technology in ultra-modern facilities.
It is worth noting that our A CUT ABOVE® diamonds may have slightly different dimensions from those stated above. We focus on maximizing perfect optical symmetry; this enables the diamond to reflect, refract and return to the eye the maximum quantity and quality of light technically possible.
The ultimate treasures are found in the A CUT ABOVE® Collection Series featuring DEF IF-VVS super ideals.

Most Popular Engagement Ring Diamond Carat

It may come as no surprise that 1 carat is the average diamond size purchased in the US for engagement rings. Because the 1 carat mark is so iconic, the weight is proportionally more expensive than, for example, a 0.90 carat diamond.
Ritani 1RZ7286 Knife-Edge Solitaire Engagement Ring
1.095ct Carat Round Dimaond Engagement Ring
The 1 carat diamond is the perfect size for almost every hand, and its range of qualities allows it to be affordable for a multitude of budgets. A 1 carat diamond can be set in almost every ring setting, giving you endless style options.
When choosing a diamond for an engagement ring, you should strive for balance and not just base your decision solely on the size of the center stone.
Selecting an engagement ring should be fun, not challenging, which is why we offer guides for other popular ring sizes:
Our inventory of loose diamonds and our in-house A CUT ABOVE® range of super ideal cut diamonds are the perfect centerpieces for our beautiful collection of designer settings.
Here at Whiteflash, we also provide a personal consulting service for customers, allowing our diamond experts to offer support so you can shop with confidence. We understand that each individual has their own set of criteria and their own particular budget that they are working with.
To help you visualize and fully understand the diamonds that catch your eye, we have friendly and knowledgeable specialists who are able to provide you with images and answer all your questions.

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