Diamond Weight Calculator

Created by Hanna Pamuła, PhD
Reviewed by Małgorzata Koperska, MD and Adena Benn
Last updated: Feb 02, 2023

If you are looking for the perfect diamonds for the engagement ring or fabulous earrings, check out this diamond weight calculator, which can help assess this desirable gem's weight. Choose between a dozen different shapes - 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 if you want to know more about diamond weight formulas. Also, we firmly believe that you will find this ring size converter useful.

Remember this bit of 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 for weighing the gemstones - although their mass is not unusually constant compared to other plant 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; and
  • Fluorescence.

Remember that the price of the diamonds is not increasing proportionally with their 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 be more than 200 million dollars. That's definitely more than the price of a hundred 1-carat diamonds or fifty 2-carats, which are the popular choice for the diamond used on engagement rings.

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 increasingly popular recently, as they are usually less expensive than an equivalent round-shaped diamond.

Diamond shapes.

How to calculate the diamond weight?

We are still hesitating: what should we choose - a heart-shaped diamond or a pear-shaped 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 a 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 percent. 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 a similar size of heart-shaped diamond. Speaking of weight, do you wonder how much value molten gold would have? Check our gold melt calculator. Are you looking to make a gold broach and need to know how much gold you will need? Visit our gold weight calculator.

Girdle thickness and diamond correction factors

Suppose you want to be even more accurate in your diamond weight estimate. In that case, you can consider two other factors influencing the final diamond weight: girdle thickness and shape correction factor.

A girdle is the 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; and
  • >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%; and
    • Marquise, Oval, Heart: +1% to +10%.
  • Large Culet

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

    • Emerald: -1% to -5%; and
    • 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; and
  • Trillion: Length × Width × Depth × 0.0057 × GT × WC.

Length to Width Ratio

Adjustment 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 Ratio

Adjustment 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 Ratio

Adjustment 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 Ratio

Adjustment 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
Diamond shape
Round
diamond illustration
Diameter
mm
Depth
mm
Adjustments (optional)
Girdle Thickness
%
Estimated Diamond Weight
carats
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