How To Calculate Diamond Carat Weight

Carat weight is one of the most important factors when looking to sell, buy, or evaluate a diamond. One of the 4 Cs of diamond grading, diamond weight is a crucial attribute of your stone. If you do not know the weight of your diamond, you may be wondering: how can I calculate diamond carat weight? Read below to learn more about diamond weight and how to calculate it, including answers to some of the most commonly asked questions regarding diamond weight:

Calculate Diamond Carat Weight

What Is Carat Weight?

Carat is a unit of measurement used to weigh diamonds and other stones. Contrary to popular believe, carat weight denotes weight, not size. A single carat is equivalently to 0.2 grams, or about the weight of a raindrop. Carat is the standard unit of measurement across the jewelry and gem industry.

How Can I Calculate Carat Weight?

The quick answer is that without the proper specialized tools, it can be difficult to get an accurate measurement of your diamond’s carat weight at home. However you can determine the approximate weight of your diamond with our free online diamond weight calculator. Using the diamond shape, length, width, and height, myGemma will provide an estimate of your diamond’s carat weight, rounded to the nearest hundredth.

what is diamond carat weight

How Is Diamond Weight Measured?

Carats are a tiny unit of measurement and even a small discrepancy in diamond weight can drastically impact the value of a stone. Because of this, carat weight is typically measured to the thousandth of a carat and then rounded to the nearest hundredth. Specialized measuring tools are often used to ensure precise, accurate measurements.

Carat weight refers to the weight of a single stone, whereas total carat weight refers to the weight of all of the stones on an item of jewelry.


  • Carat weight is often abbreviated to “ct” (or “CT”).
  • Sometimes carat weight is denoted as “cw” (or “CW”) or diamond weight, “dw” (or “DW”).
  • Total carat weight is often abbreviated as “ctw” (or “CTW”), “tw” (or “TW”), or diamond total weight, “dtw” (or “DTW”).

Is Carat Weight Related To Diamond Size?

Carat weight does not directly correlate to size. Though, typically, the more a diamond weighs, the larger it will appear, this does not tell the whole story. While a 300-carat stone will certainly be larger in size than a 3-carat stone, there is no precise correlation between diamond weight and size. Two diamonds of the same weight can have a dramatically different look and size.

Example: A 2-carat diamond with a high depth and small diameter may appear much smaller than another 2-carat diamond with low depth and a large diameter. This is because different shapes of diamonds with the same weight will often appear to be drastically different sizes.

How Does Carat Weight Affect Diamond Price?

The bottom line is that the greater the carat weight, the more a diamond is worth. In 2013, the largest diamond ever sold at auction, a 118-carat gem, was purchased for a whopping $30.6 million. This record-breaking sale is evidence of the high value of large diamonds.

Carat weight is one of the largest determinants of the value of your diamond. Along with color, cut, and clarity, diamond weight is one of the 4 Cs used to assess diamond quality and value. Larger diamonds are much rarer and harder to find than smaller diamonds, and consumers generally desire larger stones over smaller stones. Due to the rarity of larger stones, as weight increases, price-per-carat also increases significantly (all other things being equal).

There are some nuances to how diamond weight affects value. Many consumers are interested in purchasing a diamond that they can claim is 1 carats, 2 carats, 3 carats, etc. Therefore, a diamond weighing .99 carats will be much less valuable than a 1 carat diamond and a 1.99 carat diamond will be much less valuable than a 2 carat diamond.

But remember that while carat weight can have a significant effect on the value of a diamond, there are still many other factors that impact price.

large diamond record

Why Is Diamond Weight Measured In Carats?

The history of diamond weight extends as far back as Ancient times. Early gem traders used carob seeds as units of measurement to weigh their gems. They choose carob seeds as they varied little in weight and were light enough to measure differences in small stones. The word “carat” stems from the word carob.

It was later realized that carob seeds can vary significantly in weight depending on region. This meant that the carob seed system was not an accurate measuring tool. As a result, in 1907 a meeting was held: the General Conference on Weights and Measures, an official global conference to discuss worldwide physical measurements. Here the carat was defined as weighing 200mg.

In 1913, the carat weight was officially adopted as the unit of measurement for diamonds and other gemstones in the United State. And it quickly spread to global usage.

How Can I Sell My Diamond?

This carat weight estimate can be particularly useful if you are looking to sell your diamond online. myGemma offers a free, secure service for selling your diamonds, designer jewelry, luxury watches and handbags from the comfort of your own home.

Simply fill out the online form and provide some basic information about your diamond. Include the estimated carat weight, and a member of our team will be in touch with a price quote. myGemma is a BBB A+ rated diamond buyer.