How to Choose the Perfect Diamond Carat Size

As with most things people sell, the worth of diamonds has to be measured to determine the cost of each stone. Contrary to popular belief, a diamond’s carat has little to do with size. It’s more about weight. Carat weight is one of the four parameters by which sellers measure diamond value, the others being clarity, cut, and color. You must know how the carat size matches up to the physical size of each stone.

Diamond Carat Size Guide Overview

Carat is the official unit of measurement that jewelers use to estimate the size of a diamond. However, carat does not deal with the measurement of a diamond’s physical appearance, that is, length, breadth, and height. Instead, carat focuses on the weight of the stone.

Because carat focuses on the weight of the stone and weight cannot be estimated using sight, a size guide is essential. The carat size guide will help you estimate the size of a diamond if it weighs a certain amount of carats. 

In other words, you can think of the size guide as a sort of weight-to-size converter for diamonds. This converter will help you know what size will fit your jewelry perfectly.

Different Diamond Size Guides For Different Shapes

One factor that plays a crucial role in drawing up a diamond size guide is the shape of the diamond. Diamonds can have different shapes, and some shapes look heavier than they are and vice versa. As a result, there is no one-size-fits-all diamond carat size guide; instead, there is a separate guide for different shapes.

However, the tables below emphasize the most popular diamond shapes. This article will focus on shapes: Round, Princess, Cushion, Oval, Emerald, Heart, Pear, Marquise, Asscher, and Radiant. These ten shapes are the ones you would see on the most sought-after jewelry in every jewelry store.

1. Round Cut Diamond Size Guide

Over two-thirds of all diamonds sold are in the round cut, making it the most popular diamond shape. The Round Brilliant Cut has a brilliant white light reflection resulting from 58 facets (including the culet). Round brilliant cuts have a traditional, uniform, and symmetrical shape, and jewelers frequently use them in necklaces, engagement rings, and other fine jewelry.

Round MM Size	Round Carat Weight
4.0mm	0.25 ct
5.1mm	0.5 ct
5.8mm	0.75 ct
6.4mm	1.0 ct
6.9mm	1.25 ct
7.3mm	1.5 ct
7.7mm	1.75 ct
8.1mm	2.0 ct
8.5mm	2.25 ct
8.9mm	2.5 ct
9.0mm	2.75 ct
9.3mm	3.0 ct
9.5mm	3.25 ct
9.75mm	3.5 ct
9.9mm	3.75 ct
10.1mm	4.0 ct
10.43mm	4.25 ct
10.63mm	4.5 ct
10.83mm	4.75 ct
11.01mm	5.0 ct

2. Princess Cut Diamond Size Guide

The second most popular shape after rounds is the square-shaped princess-cut diamond. Princess cut stones are beautiful and feature up to 76 tiny facets and a square (sometimes rectangular) form with pointed corners.

Princess MM Size	Princess Carat Weight
3.25 mm.	0.26 ct.
4.5 mm.	0.50 ct.
5 mm.	0.75 ct.
5.5 mm.	1.00 ct.
6 mm.	1.25 ct.
6.5 mm.	1.50 ct.
6.75 mm.	1.75 ct.
7 mm.	2.00 ct.
7.5 mm.	2.50 ct.
7.75 mm.	2.74 ct.
8 mm.	3.00 ct.
8.25 mm.	3.24 ct.
8.5 mm.	3.67 ct.
8.75 mm.	4.10 ct.
9 mm.	4.12 ct.
9.5 mm.	5.09 ct.

3. Cushion Cut Diamond Size Guide

The cushion-cut diamond has square edges and rounded corners, similar to a pillow (hence the name). This traditional cut was the most often used diamond form for the first century of its existence, similar to the round cut today.

Cushion MM Size	Cushion 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.	3.50 ct.
9 mm.	4.12 ct.
9.5 mm.	5.09 ct.

4. Oval Cut Diamond Size Guide

Although oval-cut diamonds are just an extended round brilliant cut, there is much more to the allure of these loose diamonds. Oval cuts offer a more distinctive shape and, if cut correctly, might appear bigger than a round diamond.

Oval MM Size	Oval Carat Weight
3.6×2.7 mm.	0.10 ct.
5×3.5 mm.	0.25 ct.
6×4 mm.	0.50 ct.
7×5 mm.	0.75 ct.
7.7×5.7 mm.	1.00 ct.
8×6 mm.	1.25 ct.
8.5×6.5 mm.	1.50 ct.
9×7 mm.	2.00 ct.
10×8 mm.	2.50 ct.
12×8 mm.	3.00 ct.
11×9 mm.	3.85 ct.
12×10 mm.	5.05 ct.

5. Emerald Cut Diamond Size Guide

The emerald cut is a classy diamond form, often known as a square emerald cut. This diamond cut is so-called because that shape was initially designed for emeralds; however, it soon gained popularity as a diamond cut. The lengthy facets and broad table of an emerald-cut diamond make its appearance unique.

Emerald MM Size	Emerald Carat Weight
3×2 mm.	0.10 ct.
4×3 mm.	0.20 ct.
6×4 mm.	0.50 ct.
6.5×4.5 mm.	0.75 ct.
7×5 mm.	1.00 ct.
7.3×5.3 mm.	1.25 ct.
7.5×5.5 mm.	1.50 ct.
8×6 mm.	1.75 ct.
8.5×6.5 mm.	2.00 ct.
9×7 mm.	2.50 ct.
10×7.5 mm.	3.00 ct.
9.5×7.5 mm.	3.21 ct.
10×8 mm.	3.79 ct.
11×9 mm.	5.21 ct.

6. Heart Diamond Size Guide

As its name suggests, the heart diamond has a heart shape. The unique cut of the heart diamond means people mostly use it for pieces of jewelry that are supposed to serve as romantic gestures, such as an engagement ring. This fancy cut has 56-58 facets, making it a brilliant diamond for the way it reflects light.

Heart MM Size	Heart Carat Weight
4 mm.	0.25 ct.
5 mm.	0.50 ct.
6 mm.	0.75 ct.
6.5 mm.	1.00 ct.
7 mm.	1.25 ct.
7.5 mm.	1.50 ct.
8 mm.	2.00 ct.
8.5 mm.	2.50 ct.
9 mm.	3.00 ct.
10 mm.	3.50 ct.
11 mm.	4.41 ct.
12 mm.	5.66 ct.

7. Pear Diamond Size Guide

The pear diamond is distinct from all other diamond cuts, and people often refer to it as the teardrop or pendeloque cut. A modified brilliant cut combines the Marquise and oval shapes with one rounded end and a point on the other. Its distinctive silhouette is well-known and easily recognizable.

Pear MM Size	Pear Carat Weight
5×3 mm.	0.25 ct.
6×4 mm.	0.50 ct.
7×5 mm.	0.75 ct.
7.7×5.7 mm.	1.00 ct.
8×6 mm.	1.25 ct.
8.5×6.5 mm.	1.50 ct.
10×6 mm.	1.71 ct.
9×7 mm.	2.00 ct.
10×8 mm.	2.50 ct.
11×8 mm.	2.70 ct.
12×8 mm.	3.00 ct.
12×7 mm.	3.12 ct.
12×9 mm.	3.44 ct.
14×8 mm.	4.00 ct.
14×9 mm.	4.25 ct.
15×9 mm.	5.06 ct.

8. Marquise Diamond Size Guide

The modified brilliant-cut marquise diamond has a football-like form. French King Louis XIV purportedly had a stone carved to replicate what he thought was the perfectly-shaped mouth of the Marquise of Pompadour, hence the name. Marquise diamonds can give the appearance of being larger because they are long and narrow.

Marquise MM Size	Marquise Carat Weight
6×3 mm.	0.25 ct.
8×4 mm.	0.50 ct.
9×4.5 mm.	0.75 ct.
10×5 mm.	1.00 ct.
11×5.5 mm.	1.25 ct.
12×6 mm.	1.50 ct.
13×6.5 mm.	2.00 ct.
14×7 mm.	2.50 ct.
15×7 mm or 14×8	3.00 ct.
15×7.5 mm.	3.25 ct.
16×8 mm.	3.86 ct.
16.5×8.25 mm.	4.00 ct.
17×8.5 mm.	4.88 ct.
17.5×10 mm.	5.50 ct.

9. Asscher Cut Diamond Size Guide

Asscher cut diamonds, also called square emerald cuts, are essentially square when viewed from above but have rounded corners to allow more light to penetrate the stone. They have a “hall of mirrors” look and can provide exceptional brilliance due to their depth, high crown, and numerous facets. The appropriate length-to-breadth ratio for them is 1 to 1.04, and they usually have 50 or 58 facets. 

Asscher MM Size	Asscher Carat Weight
4 mm.	0.39 ct.
4.5 mm.	0.50 ct.
5 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.	3.50 ct.
9 mm.	4.12 ct.
9.5 mm.	5.09 ct.

10. Radiant Cut Diamond Size Guide

Although they have a similar outline to emerald-cut diamonds, radiant-cut diamonds are far more brilliant. They are excellent alternatives for engagement rings because they prolong the finger and cost significantly less than round diamonds.

Radiant MM Size	Radiant Carat Weight
5×3 mm.	0.31 ct.
6×3 mm.	0.41 ct.
6×4 mm.	0.50 ct.
6.5×4.5 mm.	0.75 ct.
7×5 mm.	1.00 ct.
7.3×5.5 mm.	1.25 ct.
7.5×5.8 mm.	1.50 ct.
8×6 mm.	2.00 ct.
8.5×6.5 mm.	2.25 ct.
9×7 mm.	2.50 ct.
9.5×7.5 mm.	3.00 ct.
10×8 mm.	3.50 ct.
11×9 mm.	5.05 ct.