Diamond Weight Calculator

Created by Hanna Pamuła, PhD candidate
Reviewed by Małgorzata Koperska, MD
Last updated: Apr 30, 2022

If you are looking for the perfect diamonds for the engagement ring or marvelous earrings, check out this diamond weight calculator which can help you to assess the weight of this desirable gem. Choose between a dozen of different shapes - such as, e.g., heart-shaped diamonds or pear shaped diamonds - to find the one you need. Keep reading if you are wondering what a diamond carat weight is or you want to know more about diamond weight formulas. Also, we strongly believe that you will find this ring size converter useful.

Remember about friendly advice from Marilyn Monroe: Diamonds are a girl's best friend 💎

What is a carat?

Carat is a unit of mass used for measuring gemstones and pearls. It took its name from carob tree seeds that were used for centuries as a standard of weighing the gemstones - although their mass is not unusually constant in comparison to other plants seeds. The carat unit was standardized more than a century ago, and it's now equal to 200 mg.

  • 1 carat = 200 mg = 0.2 g
  • 1 carat = 0.007055 oz

What's the 1-carat diamond price?

Unfortunately, we can't answer this question without additional information. The most obvious feature that affects the gemstone price is its weight in carats, and our diamond weight calculator can find the approximate weight of the chosen size and shape gem. However, you can't estimate the diamond ring cost on that basis, as it's only one of the few factors affecting the diamond value. The essential diamond features are:

  • cut and shape
  • carat weight
  • clarity
  • color
  • GIA cut grade
  • fluorescence

Remember that the price of the diamonds is not increasing proportionally with its weight - a 3-karat diamond will cost more than three 1-carat diamonds. Have you heard about the famous Koh-i-Noor diamond, which is a part of the British Crown Jewels? It's one of the largest cut diamonds in the world, weighing 105.6 carats, and its value is estimated to more than 200 million dollars. That's definitely more than the price of a hundred of 1-carat diamonds or fifty of 2-carats, which are the popular choice for engagement ring diamonds.

Diamond shapes

Diamonds come in many different shapes and sizes. The most popular form is the round diamond - this classic represents 3/4 of all diamonds sold. The other fancy-shaped diamonds are getting more and more popular recently, as they are usually less expensive than an equivalent round shaped diamond.

Twelve popular diamond cut shapes

How to calculate the diamond weight?

We are still hesitating: what should we choose - a heart-shaped diamond or a pear-shape diamond? Let's check what's the weight of the diamond we would like to have:

  1. Select the diamond shape. You can choose between twelve different shapes. Let's assume you want to check the weight of a pear-shaped diamond.
  2. Enter the diamond's dimensions. Type its length, width, and depth, or diameter and depth if you've chosen the round diamond. Take as an example the pear shape diamond 6 mm long, 4 mm wide with depth (height) equal to 3 mm.
  3. Check the ring girdle. If it's thin, you don't need to change anything, for thicker you may want to add a few percents. Assume that our exemplary diamond has a medium girdle, so let's type, e.g., 2%.
  4. Find out if the diamond shape is standard. Our pear-shaped diamond has wide wings, so we enter 5%.
  5. Diamond weight calculator displays the diamond weight in carats. It's 0.45 carats in our example.

Now find out for yourself what's the weight in carats for the similar size of a heart-shaped diamond. Speaking of weight, do you wonder how much value molten gold would have?

Girdle thickness and diamond correction factors

If you want to be even more accurate in your diamond weight estimate, you can take into account two other factors influencing the final diamond weight: girdle thickness and shape correction factor.

A girdle is an outermost edge of the diamond. It is expressed as a percentage of the average diameter or described in the rating scale (thin, medium, thick, super thick, etc.). Add:

  • 0% - 1% if the girdle is very thin or thin
  • 1% - 3% if medium
  • 3% - 6% for thick and very thick girdles
  • >6% for extra thick

If your ring shape is not ideally regular and standard, you can add even other correction adjustments to the final weight formula. The popular adjustment factors for selected shape variations are:

  • Wide or fat wings, squarish or high shoulders

    • Pear: +1% to +5%
    • Marquise, Oval, Heart: +1% to +10%
  • Large Culet

    • All Shapes: +1% to +2%
  • Wide Corners

    • Emerald: -1% to -5%
    • Radiant: -1% to -5%
  • Pavilion Bulge

    • Emerald, Radiant & Trillion: +1% to +18%

Type the value in the correction factor box of the diamond weight calculator, and it will take those conditions into account when calculating the final diamond weight.

Diamond weight formulas

Our diamond weight calculator uses the following formulas to estimate the approximate carat weight:

GT = Girdle Thickness Factor, WC = Weight Correction Factor, AF = Adjustment Factor

  • Asscher: Length * Width * Depth * 0.0080 * GT * WC
  • Baguette: Length * Width * Depth * 0.00915 * GT * WC
  • Cushion: Length * Width * Depth * 0.00815 * GT * WC
  • Emerald: Length * Width * Depth * AF * GT * WC
  • Heart: Length * Width * Depth * 0.0059 * GT * WC
  • Oval: Length * Width * Depth * 0.0062 * GT * WC
  • Princess: Length * Width * Depth * 0.0083 * GT * WC
  • Round: Diameter² * Depth * 0.0061 * GT
  • Trillion: Length * Width * Depth * 0.0057 * GT * WC
Length to Width RatioAdjustment Factor
1 : 1 0.0080
1.5 : 1 0.0092
2 : 1 0.0100
2.5 : 1 0.0106
  • Marquise: Length * Width * Depth * AF * GT * WC
Length to Width RatioAdjustment Factor
1.5 : 1 0.00565
2 : 1 0.00580
2.5 : 1 0.00585
3 : 1 0.00595
  • Pear: Length * Width * Depth * AF * GT * WC
Length to Width RatioAdjustment Factor
1.25 : 1 0.00615
1.5 : 1 0.00600
1.66 : 1 0.00590
2 : 1 0.00575
  • Radiant: Length * Width * Depth * AF * GT * WC
Length to Width RatioAdjustment Factor
1 : 1 0.0081
1.5 : 1 0.0084

If the ratio of the chosen gem is not equal to the standard value from the table, the calculator uses the nearest given ratio.

Hanna Pamuła, PhD candidate
Diamond shape
diamond illustration
Adjustments (optional)
Girdle Thickness
Estimated Diamond Weight
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