Diamond Carat Size Chart – Weight to MM Conversions And Visual Comparisons

diamond carat size chart

This diamond carat size chart is based on ideal cut proportions and should be used only as a reference for relative comparison only. Take note: the actual size of the stone may vary due to different computer screen resolutions.

Carat refers to the weight of the diamond and not the physical dimensions it possess. Two diamonds’ dimensions can differ even though they have the same weight. For example, a 1 carat round diamond that is ideally cut will measure up at 6.50 mm. On the other hand, a 1 carat diamond that is cut deeply could have a diameter of 6.20 mm.

hidden weight

Illustration of two 1 carat diamonds to relative scale.

Also, most people have misconceptions that a diamond of 3.00 carats would be twice as big as another stone of 1.50 carats. This isn’t true. As you can see from the chart above, a 3.00 carat diamond would have a diameter of 9.00 mm compared to the 7.50 mm diameter a 1.50 carat diamond has. The 3 carat stone is only twice as heavy and not twice as big!

Free Bonus: Download a printable carat size chart that will show you exactly how diamonds will look like in real life. All images are precisely drawn to scale. Includes additional bonus diamond buying tips and strategies.

Reference Table of mm Conversions For Popular Sizes – Round Cuts

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
4.10 x 4.10 0.25 6.20 x 6.20 0.90
5.20 x 5.20 0.50 6.50 x 6.50 1.00
5.40 x 5.40 0.60 7.40 x 7.40 1.50
5.80 x 5.80 0.75 8.20 x 8.20 2.00
70 pointer SI2 solitaire round
1.01 carat round diamond
2.40 carat stone size estimation

From left to right: 0.70, 1.01 and 2.40 carat round cuts on 2.5mm platinum rings.

To see engagement rings that other people had purchased, click here to check out our image gallery.

Visualizing Diamond Sizes on a Hand to Scale

James Allen has an interesting graphic illustration of how rings with different diamond sizes would look like when viewed on the hand. Click here to find out more…

finger simulation with different carat sizes

What About Size Proportions for Fancy Cut Diamonds?

Before we show you the conversion tables for fancy cuts, you need to take note that the dimensions shown here are based on “ideal” length to width proportions.

If you do a quick check in stores or via online inventories, the dimensions you see will vary from stone to stone depending on the l/w ratio. Ultimately, the length to width ratio of a fancy cut is chosen based on your personal preference. length to width ratios of heart cut diamonds To put things in perspective, the dimensions of a 1 carat heart shaped diamond would be 6.50mm x 6.50mm. This is based on a length to width ratio of 1:1. Most people (including myself) prefer fatter looking stones in the range of 0.90:1 length to width ratio. Needless to say, the dimensions of a heart diamond would no longer be 6.50mm x 6.50mm.

To cite an example, a heart shaped diamond with 0.90 length to width ratio might exhibit a dimension of 6.15mm x 6.80mm and is perfectly acceptable.

   
   

Carat Weight to MM Conversion for Fancy Cuts

Princess Cut Diamonds

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
3.40 x 3.40 0.25 5.50 x 5.50 1.00
4.35 x 4.35 0.50 6.00 x 6.00 1.25
4.75 x 4.75 0.63 6.50 x 6.50 1.50
5.10 x 5.10 0.75 7.50 x 7.50 2.00

Oval Cut Diamonds

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
5.00 x 3.00 0.25 7.50 x 5.50 1.00
6.00 x 4.00 0.50 8.00 x 6.00 1.25
6.50 x 4.50 0.65 8.50 x 6.50 1.50
7.00 x 5.00 0.75 9.00 x 7.00 2.00

Marquise Cut Diamonds

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
5.30 x 2.65 0.25 10.40 x 5.20 1.00
8.00 x 4.00 0.50 11.20 x 5.60 1.25
8.70 x 4.35 0.65 12.00 x 6.00 1.50
9.20 x 4.60 0.75 13.10 x 6.55 2.00

Pear Cut Diamonds

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
4.50 x 3.00 0.25 8.40 x 5.60 1.00
6.00 x 4.00 0.50 8.70 x 5.80 1.25
6.80 x 4.53 0.65 9.00 x 6.00 1.50
7.50 x 5.00 0.75 10.00 x 6.67 2.00

Cushion Cut Diamonds

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
3.50 x 3.50 0.25 6.20 x 6.20 1.00
4.85 x 4.85 0.50 6.60 x 6.60 1.25
5.40 x 5.40 0.60 7.30 x 7.30 1.50
5.80 x 5.80 0.75 7.60 x 7.60 2.00

Emerald Cut Diamonds

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
5.00 x 3.33 0.25 6.90 x 4.60 1.00
6.00 x 4.00 0.50 7.40 x 4.93 1.25
6.20 x 4.13 0.60 8.10 x 5.40 1.50
6.50 x 4.33 0.75 8.70 x 5.80 2.00

Asscher Cut Diamonds

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
3.40 x 3.40 0.25 5.50 x 5.50 1.00
4.35 x 4.35 0.50 6.00 x 6.00 1.25
4.75 x 4.75 0.63 6.50 x 6.50 1.50
5.10 x 5.10 0.75 7.50 x 7.50 2.00

Radiant Cut Diamonds

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
4.30 x 3.23 0.25 6.90 x 5.19 1.00
5.60 x 4.21 0.50 7.25 x 5.45 1.25
6.00 x 4.50 0.65 7.55 x 5.68 1.50
6.20 x 4.66 0.75 8.30 x 6.24 2.00

Trilliant Cut Diamonds

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
4.10 x 4.10 0.25 6.80 x 6.80 0.90
5.40 x 5.40 0.50 7.20 x 7.20 1.00
5.70 x 5.70 0.60 7.40 x 7.40 1.50
6.35 x 6.35 0.75 8.20 x 8.20 2.00

Heart Cut Diamonds

Dimensions (mm) Carat Weight Dimensions (mm) Carat Weight
4.00 x 4.00 0.25 6.50 x 6.50 1.00
5.00 x 5.00 0.50 7.00 x 7.00 1.25
5.90 x 5.90 0.75 7.50 x 7.50 1.50
6.20 x 6.20 0.90 8.00 x 8.00 2.00

Disclaimer: Choosing a beautiful fancy cut diamond cannot be done based on dimensions or grading reports alone. While dimensions can help you weed out badly cut stones, you should view (magnified) photographs/videos to determine the personality of the diamond. The overall outline, locations and types of inclusions are all factors that play an important role in its appeal.

Also, you should view ASET images when selecting a fancy cut diamond in order to determine its optical performance. For shapes like ovals, marquises and pears, it is best to seek the help of a professional to determine the extent of the bowtie effect. If you intend to buy a fancy cut diamond, this guide is indispensable.

Size Isn’t Everything. Cut Is.

All in all, the millimeter dimensions of a diamond is very useful information as it gives you a rough idea how big the stone would look on a finger. To complete the selection process, you need to go beyond the 4Cs that are shown in a lab report.

Apart from estimating how a stone with a specific carat weight would measure up physically, did you know that you can decipher more details based on weight alone? On the next page, we will show you how to apply some basic reverse engineering and perform critical analysis on your diamond.

Don’t Forget: Download a printable carat size chart that will show you exactly how diamonds will look like in real life. All images are precisely drawn to scale.


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