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Diamond Sizes: A Handy Guide

by Molly Jones
Last updated on August 21, 2023

When it comes to diamond sizes, is bigger always better? How do you accurately measure diamonds? How much does diamond size actually influence the diamond’s price?

Shopping for a diamond can be confusing. That’s why we created this handy guide that covers the ins and outs of everything diamond size.

How Are Diamond Sizes Measured?

Modern Sapphire Halo Ring available in various diamond sizes.

When shopping for diamonds, you may have heard of two different units of measurement: carat and millimeter. While you may have heard them used interchangeably they are definitively not the same. We’ve broken down just what exactly the carat size and millimeter size of your diamond means for you below.

What Is the Carat Weight of Diamonds?

3/4 CT Pink Oval Solitaire Pendant available in various diamond sizes.

Carat weight is a measure of mass that tells you how much your diamond weighs. A diamond that is 1 carat weighs exactly 200 milligrams. The more carats a diamond has, the heavier it will be—and the more expensive. So if you’re looking for a larger diamond but don’t want to spend too much money, go with a smaller carat weight stone instead of a larger one with a lower grade of cut or clarity rating. Don’t know much about clarity? Check out our diamond clarity chart.

What Is the MM Size of Diamonds?

Trinity Classic Ring available in various diamond sizes.

Millimeter size is measured in mm (millimeters). It refers to the diameter of a diamond—the distance across its widest point when viewed from above or below. This measurement is used when describing mounted diamonds.

Diamond Millimeter Size Measurement vs. Diamond Carat Weight Measurement

Borealis studs available in various diamond sizes.

Because millimeter measurements of diamonds are measurements of the diamond’s diameter across the surface, larger millimeter sizes of diamonds will always appear true to size.

On the other hand, because a diamond’s carat weight is a measurement of the diamond’s weight and not size, it is possible for the diamond to seem to appear either larger or smaller than its carat weight.

For example, a 1-carat round brilliant cut diamond with a cut grade of Z will seem smaller than a similar 1-carat round brilliant cut diamond with a cut grade of D.

Why? The cut quality will affect the perception of size. If the Z-graded diamond carries a majority of its weight on the lower half of its girdle, it will have less surface area than an otherwise similar D-graded diamond that has more even distribution across its girdle.

Diamonds can appear larger than their carat weight due to their shape. This is because of the millimeter size of the face of the diamond. For example, a 1-carat diamond that is marquise shaped will have a millimeter size of 10 x5 mm while an oval-shaped 1-carat diamond will have a 7.7 x 5.7 mm size.

Use a Diamond Sizes Chart to Easily Convert Carat Weight to MM Sizes

St. Tropez Ring available in various diamond sizes.

When in doubt a handy diamond size chart can easily be found online. A diamond size chart contains the carat weight of a diamond and its corresponding mm size and deviation per shape.

A diamond size chart is a fast and accurate way to determine what measurement might be more useful to consider when searching for a diamond. The diamond size chart is a standard fixture in many jewelry stores, but you can as easily find them online.

Should I Use MM Sizes or Carat Weight Sizes When Shopping for Diamonds?

Czarina Bridal Set available in different diamond sizes.

When shopping for diamonds consider both carat size and mm size.

If you want a bigger stone that costs less money, you might want to go with one that has a higher mm size value and a lower carat weight value.

For example, let’s say you’re shopping online and see two diamonds that have similar millimeter sizes but different carat weights. It’s likely that one will be less expensive than the other because it has fewer carats and therefore weighs less overall. However, despite this, it will still appear to be larger.

Additionally, it’s equally important to consider the carat weight because it is a determining factor in a diamond’s overall grade and cost. Many people want the glitz factor of being able to say that they have a 1-carat diamond. Plus, mm size is less important than carat weight for some shapes of diamonds over others.

Ultimately, diamond experts agree that the best practice to employ when shopping for diamonds is to take into consideration both systems of measurements in addition to desired ring shapes. When you do this you can be sure you will select the perfect diamond that will appeal to the naked eye.

How Does a Diamond’s Shape Affect Different Diamond Sizes?

1 1/2 ct. tw. Blue Cushion Stud Earrings--also available in other diamond sizes.

Different diamond shapes affect the appearance of a diamond’s size in different ways. In fact, the overall size of the diamond is determined by its cut, which in turn, is determined by its style.

For example, marquise cut diamonds appear larger than their actual carat size. This is thanks to their long table surface and high mm size. Read on to discover how mm size can affect the appearance of diamonds of the same carat weight.

Round Brilliant Cut Diamond

Plié Halo Ring available with various diamond sizes.

A round diamond is one of the more popular diamond shapes due to its everlasting appeal and timeless sparkle. A round diamond should have a depth percentage of around 63%. This results in light being able to enter and exit the diamond freely, thus creating its characteristic shine.

Round cut diamonds are the classic diamond style. A round diamond’s millimeter size is not as important because its value is based more on its carat size. Round diamonds maintain an accurate naked-eye view of the carat size.

Asscher Cut Diamond

Antique Solitaire Ring available in various diamond sizes.

The Asscher cut style is a step-cut style that is a variation of the princess cut. It has 58 facets and a rectangular shape, with beveled corners. Diamond cutter Joseph Asscher created the Asscher cut style in 1902.

As the Asscher shape is within the square family, well-cut diamonds will appear accurate to their carat weight. Thus, Asscher cut diamonds that have a carat weight of one will appear true to size. As the carat weight increases so does the appearance of the diamond.

Cushion Cut Diamond

Grace Classic Ring available in various diamond sizes.

The cushion style diamond has a round shape with smooth sides and a flat bottom. The top and bottom of the diamond curves inward, and it resembles a pillow or cushion–hence its name!

Cushion cut diamonds are available in many diamond sizes, ranging from 0.10 carats to 1.50 ct and up. Like other square shapes, the cushion style appears true to size.

Princess Cut Diamond Shape

Opera Ring with princess cut diamond--available in various diamond sizes.

A princess diamond is a square-ish shape with small facets on the corners. The shape of a princess cut diamond can make it appear larger than it actually is. For example, if you have a 1.50 ct princess shape diamond, and you compare it with a 1.50 ct round diamond, the princess cut will appear larger than the round brilliant because of its square shape.

However, if you compare them both at 0.5 carats, the difference in size will be much less noticeable. Why? Because both diamonds are more similar in size at that point.

Oval Shape Diamond

Denmark 3 Stone Ring in rose gold setting with oval-shape diamond.

An oval-shaped diamond will appear slightly larger than similar carat weights of square diamonds or the round diamond. This is because an oval diamond is wider than it is tall, and therefore has more surface area than a round stone of the same size.

What Diamond Sizes Are Right for You?

1 1/2 ct. tw. Classic 3 Stone Pendant

It’s not always easy to know what size and shape of diamond is right for you. Here are some tips to help you decide:

Consider How Much You Want to Spend

First, think about how much money you want to spend on diamonds—and really, any piece of jewelry—and then set aside a little extra for future maintenance costs. While it’s true that diamonds are forever, they do require some upkeep!

Make a List of Your Priorities

For example, if you want a big diamond but don’t have much money, then maybe you want to look into smaller stones instead of large ones with low quality. If your budget is more flexible and you want something big, then focus on finding good quality diamonds that have a larger surface area. The options are endless when it comes to choosing a diamond; just make sure they’re within your price range!

Consider What Will Be Worn With It

If you’re getting married, then chances are people will see this ring every day—so it should be something special and memorable! If this isn’t something that will be worn often or something that will be worn on only special occasions, then maybe choose something smaller so there’s less risk of losing or damaging it—but still something that shows off your style!

Try On Different Diamond Sizes

Start at a 0.50 ct and see how it feels and looks like on your finger. If you want to continue sizing up go up a half-carat. Continue until you find a physical size that works for you.

Don’t Focus on Price

Sure, it makes sense to get something within your budget range. But don’t get yourself stuck on finding “the perfect deal.” Remember: there is no such thing as perfection.

Clean Origin Can Help You Find the Perfect Diamond Sizes

Crescendo ring in 14k yellow gold with round cut diamond.

Clean Origin has a broad range of premium lab diamonds in a stunning selection of styles that vary greatly from 0.02 carat to 9! Plus, we have a 100-Day Return Policy. Should you feel that your engagement ring could use more bling you are welcome to return the ring and focus your search on finding a larger diamond carat weight.

Whether you’re looking for a round diamond, an Asscher style, or a pear-shaped beauty we have a diamond that will fit your needs.