How To Calculate Diamond Carat Weight

When it comes to selling, buying, or assessing a diamond, carat weight stands out as one of the most significant factors to consider. As one of the four Cs of diamond grading, the weight of a diamond holds immense importance in determining its overall value. If you find yourself uncertain about the weight of your diamond, you might be wondering: How can I calculate the carat weight of a diamond? Let’s discuss diamond weight and explore how to calculate it effectively while addressing some frequently asked questions related to this crucial aspect.

Diamond carats explained

Carat weight refers to the unit of measurement used for weighing diamonds and other precious stones. It is important to note that carat weight primarily signifies the mass of a diamond, rather than its physical size. Specifically, one carat is equivalent to 0.2 grams, which is approximately the weight of a small raindrop. Carat weight serves as the standardized unit of measurement within the jewelry and is especially important in the case of loose diamonds. You can get more information about carat weight in our other article “A Brief Idea About Carat Diamond Weight

Steps to calculate diamonds carat weight

Determining the carat weight of a diamond involves a systematic process that takes into account specific measurements. Here are the steps to calculate the carat weight of a diamond:

Step 1

Measure the Diameter: Use a millimeter ruler or a digital caliper to measure the diameter of the diamond. Ensure that you measure the widest point across the diamond.

Step 2

Convert Diameter to Average Radius: Divide the diameter measurement by two to obtain the average radius of the diamond.

Step 3

Calculate the Volume: The volume of a diamond can be approximated by using the formula for the volume of a sphere, which is (4/3) * π * (radius^3). Calculate the volume using the average radius obtained in step 2.

Step 4

Apply Diamond Density: The density of a diamond is approximately 3.52 grams per cubic centimeter. Multiply the volume of the diamond by the diamond density to calculate its approximate weight in grams.

Step 5

Convert to Carat Weight: Since one carat is equivalent to 0.2 grams, divide the weight in grams obtained in step 4 by 0.2 to determine the carat weight of the diamond.

It is important to note that these calculations provide an estimate of the carat weight, and the precise measurement may vary due to factors such as cut, shape, and depth of the diamond. 

Institutions such as GIA have played a pivotal role by providing standardized formulas for calculating the carat weight of diamonds based on their specific shape.

In cases where the exact weight of a mounted diamond is unknown, you can employ the diamond’s millimeter measurements to estimate its carat weight. The Gemological Institute of America (GIA) provides formulas and tables specifically designed for calculating the carat weight of mounted diamonds. Here are the essential details:

The formula for Round Brilliant Cut Diamonds:

To calculate the approximate carat weight of a round brilliant-cut diamond, you can follow the below formula: 

[average diameter x average diameter x depth x 0.0061]

You may think of the surface of the diamond as if it was a clock. Then you can measure the distance from the twelve o’clock to the six o’clock position. So let’s say it measures 6.48 mm.

Once that is done, start measuring the distance from the nine o’clock to the three o’clock position and let’s say that measures 6.51 mm. It’s time to add 6.48 to 6.51 and you get 12.99 which you then divide by two (the number of the measurements taken) and the average diameter is 6.49 mm.

Now measure the diamond from the table facet (flat facet on the top) down to the culet (bottom point). Let’s say this value is 3.98 mm and you’ll have the numbers required for the given formula. For instance:

6.49 x 6.49 = 42.1850 x 3.98 = 167.052 x 0.0061 = 1.02 carats

Similarly, we have mentioned the most essential formulae in the below chart:

The formula for Oval Brilliant Cut DiamondThe average diameter x average diameter x depth x 0.0062 = approximate carat wt.
The formula for Heart Shape Brilliant DiamondLength x width x depth x 0.0059 = approximate carat wt.
The formula for a Triangular Brilliant (Trillion) Cut DiamondLength x width x depth x 0.0057 = approximate carat wt.
The formula for an Emerald Cut, Princess Cut, and Quadrillion Cut DiamondLength x width x depth x adjustment factor (see below) = approximate carat wt.

If you want to know more about the metrics and measurements, visit for more information. 

To summarize, accurately calculating the carat weight of a diamond is crucial for determining its value and making informed decisions. Institutions like GIA have provided standardized formulas for each diamond shape, simplifying the process and ensuring consistency in evaluations. Carat weight not only serves as a basis for pricing but also enables comparisons between different diamonds, allowing individuals to select the stone that aligns with their preferences and budget. Find a reliable online store such as Uniglo Diamonds that can guide you through the entire buying process. 

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