Diamond Deep Dive: Carat Weight

Diamond Deep Dive: Carat Weight

What does carat weight really mean to a diamond? Continuing in our "Diamond Deep Dive" series, we're going to talk about diamond carat weight and how it affects the performance and appearance of a diamond.

By now, I assume you have already read the first and second parts in our series, Diamond Deep Dive: The Cut, and Diamond Deep Dive: Clarity. If you haven't yet, then be sure to check them out, too.

Kelly louping a diamond

Carat Weight

It's pretty simple. Carat weight is just a unit of weight. It's just like grams, ounces, pounds, etc. It's a very small unit of weight, however, which is why it's used for diamonds. For example, 1 carat equals 0.2 grams (1/5th of a gram). To make one pound of diamonds you would need 2,265 carats - that's a lot of diamonds!

So, how carat weight relates to a diamond is simply that that is how we "weigh" a diamond. Just like standing on your scale in the bathroom, we have very small scales that measure weight in carats.

Image of diamond scale with diamond on it

One should not confuse "carat" with "karat", however. The term karat is used to measure the purity of gold, which is why you see 14K, 18K, 24K, etc. The "K" denotes karat. But that's for another blog post, so let's stick with diamonds for now.

Carat Weight and Diamond Performance

If you're familiar with the other two articles I mentioned previously you'll know that I talk a lot about the "performance" of the diamond. The performance is simply how well that diamond reflects light back out. That reflection is what gives diamonds their signature sparkle. So far, in the previous Deep Dive articles, I have focused on how the different parts of the "4 C's" relate back to performance.

So, how then does carat weight affect the performance of the diamond? The answer is that it doesn't... What? Boring! Who cares then? Well, if you ask around, a whole heck of a lot of people care, because it relates to the resulting appearance of the diamond - the size. There are those that believe that "bigger is better", and the heavier the diamond, the bigger it is!

Given that the weight relates to the size, and given that a round diamond shape is cut pretty consistently, we can even measure a diamond using a millimeter gauge and then translate that to an approximate carat weight. For example, below is a chart that shows conversions between measurements and carat weights. You can see that as the weight goes up, the size goes up. Just remember, these conversions are an approximation. To get the true weight of a diamond we have to use the scale we talked about previously. This method works great in a pinch, or when we can't remove a diamond from its setting.

Carat Weight
Round Diamond (mm)
0.03 2.0
0.10 3.0
0.25 4.1
0.5 5.2
1.0 6.5
2.0 8.2
4.0 10.4
5.0 11.2

If you're the type that likes homework, here's an assignment for you. See if you can measure, in millimeters, one of your diamonds and then get the approximate size. Here is a full conversion chart. Bring it in to the store and we can double check your work for you.

Does Size Matter?

This is 100% a personal, and financial, choice. Does the diamond fit in the setting you would like? Are you a "showy" person, or more reserved? It all depends on the look you're going for. It is indeed the case that as a diamond gets larger, the price increases, so you will have to weigh what factors are most important in your diamond decision to find the one that "speaks to you".

Image of diamonds lined up next to each other to show sizes

When diamonds are mined (or manufactured) and sold, the price is directly related to how rare the diamond is. As a diamond gets larger, it becomes more rare, and the price goes up accordingly. When you combine multiple factors of rarity - all four C's, for example, the price can continue to climb. For some people, it's about color and clarity and that's where they want their budget to go. For others, it's about the size - the "wow factor" - so they're willing to compromise on clarity or color to get the largest diamond for their budget.

If this is all a lot to think about, don't worry. When discussing a diamond purchase with our experts they will guide you through the nuances of making those decisions and help you weigh what the most important factors are for you.

Carat Weight versus Total Carat Weight

Sometimes you will see the term "total carat weight", or "carat total weight", often abbreviated as "ctw", "cttw", and sometimes "tcw". Thus far we have talked about carat weight in the weighing of a single diamond. In the case of total carat weight that is when we are weighing multiple diamonds at once.

Image of mounting with diamonds on side

Total carat weight is often used to denote the weight of a cluster of diamonds on a mounting - what we call "melee". The image above shows a mounting with no diamond in it. That mounting contains 0.47 total carat weight of diamonds - abbreviated as ".47ctw". That is to say, when you weigh up all of those smaller diamonds together, their combined carat weight comes to 0.47. When we write an appraisal document for you it will outline the diamonds shown in the mounting as "total carat weight", and separate the center stone weight on its own.

Origins of The "Carat"

Back in the day, before fancy digital scales, and precise units of measure, traders thought that the seed of the Carob tree was pretty consistent in weight. So, when counter-balancing a scale, they would use the carob seed to conduct weight measurement of goods... Pssst, don't tell them, but this wasn't actually correct. Tests have since shown that there is as much variation in the carob seed as any other. Oops.1

To get to where we are today, 200 milligrams per carat, the measurement was proposed at the "fourth sexennial General Conference of the Metric Convention held in Paris in October 1907", and then signed into law in France. It seems England took a little longer to catch on1.

Image of Carob Tree

Image Courtesy of Wikipedia

In case you're wondering about the Carob Tree, it is a tree of the pea family. It's native to the Eastern Mediterranean2, but is pretty hardy and can grow in different environments - probably not outside here in New England, though. The pods can be ground into powder and are often used as a replacement for cocoa3.

Closing Thoughts

Our goal at Jewelry Creations has always been to not just sell a product, but to educate people on that product so that they can make the most informed decision possible and meet the goals they are trying to achieve. I hope that this blog post helped teach you a little something you didn't know about diamonds before.

Be sure to keep an eye out for the next blog post in this series, "Diamond Deep Dive: Color", as we continue on our journey exploring the "4 C's" in depth — and be sure to read the previous blog posts Diamond Deep Dive: The Cut, and Diamond Deep Dive: Clarity.

Series Links