The Highlights: Diamond Carat Size

When you come into our showroom at J. Vincent, we are happy to go over all your options when it comes to an engagement ring— whether you fall in love with something in one of our cases or would like to talk about a custom creation. That said, we respect that most couples prefer to begin their search for the perfect engagement ring where we spend most of our time lately— online.

If you’ve begun shopping for a loose diamond or an engagement ring, there is a good chance you come across the 4 C’s. Get used to hearing about these four big C’s, because as they highlight a diamond’s cut, color, clarity, and carat weight, they will greatly affect the look and cost of any stone.

Diamond sizes and how diamonds are measured is the most commonly discussed aspect of any diamond. Diamond carat size is on many wish lists, what carat a diamond is can be a question pondered when someone gets engaged, and it’s in every headline when a celebrity says “yes.” But have you ever wondered if there is more to carat size than meets the eye?

Read below for a breakdown on the carat weighing system used for diamonds and why the weight of every diamond is unique.

Why Carats?

Carats (ct) are a unit of mass used to weigh diamonds, gemstones, and pearls. The carat is a very old standard of measurement that extends back to at least the 16th century for measuring diamonds. The carat probably has its origins in the carob seed used in Greek and Roman times as a standard form of small measurement. Even though we think of carat as a measuring the size of the diamond this is not the case. The carat is a weight measurement so the appearance of two stones that are both 1 carat diamonds can be somewhat different.

Today a carat is equal to 200 mg. This standard of measurement was adopted early in the 20th Century by the General Conference of Weight and Measures (Conférence générale des poids et mesures – CGPM). Interestingly, the CGPM, established in 1875, is the same organization that established the metric system and encouraged its adoption throughout the world for the standardization of all weights and measurements.

Each carat is divisible by 100 points, each weighing 2 milligrams. Prior to the standardization and adoption of the carat system different countries used slightly different standards of measurement for diamonds and gemstones making it very difficult to compare one stone to another without placing them side by side. The adoption of the carat meant that a diamond seller in Africa and a diamond buyer in Brussels could reach an agreement concerning a particular stone much more easily.

Not All Carats Are Created Equal

However, the carat system has its limitations because diamonds are shaped and cut differently. A 1 carat diamond can be cut long and deep and it will look visibly smaller than a diamond that is cut shallower. The different cuts of the stones, for example cushion, round, marquise, square, emerald or pear will also weigh different amounts because the cuts are different. In other words, how the stone is cut and its shape can have a dramatic impact on the presentation of the stone.

The size of a diamond dramatically influences its price. This is where the carat becomes a very valuable tool. Larger diamonds are rare compared to smaller diamonds so the price per carat substantially increases based on the weight of the stone. For example, a 5 ct diamond may cost $45,000 per carat while a smaller stone less than 1/2 ct may cost $2,400 per carat for a diamond that is graded the same in all the other categories.

We invite you to shop our extensive collection of engagement rings in our Colts Neck, New Jersey, showroom, or view a selection online here.


“J Vincent jewelers exceeded all my expectations!! My fiancée and I were looking for rings and I had mentioned that i had inherited some of my grandmothers jewelry and was hoping that could be incorporated into my engagement ring. With the help of Justine at j Vincent every dream I had for my ring was exceeded!! Justine took an old fashioned ring and turned it into a perfect new looking spilt shank that was so beautiful I couldn’t even dream it up! she truly understood my vision, taste and was respectful of our budget. Professional, timely, and most importantly made you feel like you were shopping with family! I highly recommend j Vincent and Asking for Justine! — Melinda P. on Yelp