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Carat Weight Calculator

Created by Luis Hoyos
Reviewed by Komal Rafay
Last updated: Jan 18, 2024

If you need to know the weight of a specific diamond size, this carat weight calculator will greatly help. Whether you're a jewelry enthusiast, a diamond dealer, or simply curious about the value of your precious stones, calculating the carat weight of your diamonds is essential.

  • The tool uses the dimensions of the diamond in mm to calculate the carat weight for that piece of jewelry.
  • If you need to perform carat-to-gram conversions, go directly to the diamond weight and input it in carats to obtain it in grams. You don't need to input anything else.

How to use this carat weight calculator for diamonds?

To go from the dimensions of a diamond in mm to its carat weight, the calculator needs two pieces of information:

  1. The diamond shape, which will determine the formula used.
    • Most people will need to select the round shape, which comprises about 75% of all diamonds sold.
    • Nevertheless, other shapes are getting increasingly popular recently, as they are usually less expensive.
  2. The diamond dimensions:
    • For round diamonds, you'll need to input the diameter and depth;
    • For other diamond shapes, you'll need to input the length, width, and depth..

Optional values

  1. Girdle thickness (optional): For more accuracy, we can consider the thickness of the girdle of the diamond using a scale of thin, medium, thick, super thick, etc.

    • 0% - 1% Very thin or thin girdles;
    • 1% - 3% if medium;
    • 3% - 6% for thick and very thick girdles; and
    • >6% for extra thick.

    (the numbers above are the girdle percentage of the average diameter)

  2. Correction factor: For non-circular diamonds, we can even add other correction adjustments. These factors range from -5% to 18%, depending on the diamond's shape and its geometrical irregularities.

🙋 Do you need to know the math behind this tool? Look at the formulas in our diamond weight calculator.

Carat-to-gram conversion

One carat equals 0.2 grams. Therefore, to convert from carats to grams, you must multiply the weight in carats by 0.2. For example:

  • 2 carats equal 0.4 grams because:
    • 2 carats = (2 × 0.2) grams = 0.4 grams.
  • 3 carats equal 0.6 grams because:
    • 3 carats = (3 × 0.2) grams = 0.6 grams.
  • 24 carats equal 48 grams because:
    • 24 carats = (24 × 0.2) grams = 4.8 grams.

Other similar tools

Discover more about diamond calculation with these tools:


What is the weight in carat of a 1.5 mm diamond?

A 1.5 mm round diamond will weigh about 0.015 carats for a 1 mm depth. For other diamond diameters or depths, use our carat weight calculator.

What is the weight in carat of a 9x7 mm diamond?

The weight in carats of a 9×7 mm oval diamond will be between 2 and 2.5 carats, for depths between 5 and 6 mm. The exact answer will depend on the diamond depth, girdle thickness, and geometric irregularities.

Luis Hoyos
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diamond illustration
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