Use my simple, free calculator to estimate the weight of your Diamond. Simply select the shape, enter the length, width and depth (all to 2 decimal places, for example: 6.40 x 4.25 x 2.50), then click calculate.

If you aren’t sure of the girdle thickness or whether you need to add a correction, I recommend leaving these as the default options.

How Do You Estimate The Weight Of A Diamond?

The easiest way to do this quickly is to use the calculator that I created above but you can also do this manually using a weight estimation formula and different styles of cut have different formulas and adjustment factors.

What makes weight estimation more accurate than simple size-to-weight conversion charts is that in order to do weight estimation, you not only need to measurements for the diameter or length and width but also the depth of the Diamond, which is the distance between the table and culet of the stone.

And to get the most accurate measurements, you need a precise measuring tool such as a Presidium gauge or an accurate vernier gauge.

If math scares you then these formulas may seem a bit daunting but they are very easy to do as all you need are the measurements and a calculator.

Weight Estimation Formula For Round Brilliant Cut Diamonds

A Round Brilliant Cut Diamond Table Up

Due to it being the most popular style of cut, the most commonly used weight estimation formula is the one for Round Brilliant Cut Diamonds and the formula is:

  • Average Diameter¬≤ x Depth x 0.0061

To get the average diameter, ideally, you want to measure across four directions (north-south, east-west and diagonals) but this isn’t always possible when the Diamond is in a piece of jewelry and in most cases, you will only be able to measure two directions but this is fine and will still work.

You then want to get the average and multiply this by itself before multiplying it by the depth and then the adjustment factor, which is 0.0061.

Let me give you an example using the details from the GIA sample report, which gives us the measurements of:

  • Diameter: 6.41mm – 6.43mm
  • Depth: 3.97mm

To start figuring out the estimated weight would first involve figuring the average diameter (6.41 + 6.43 / 2 = 6.42mm), once you have this, you can then do the full formula:

  • 6.42 x 6.42 x 3.97 x 0.0061 = 0.998 carats

This is pretty close to the stated weight of 1.01 carats and when you add in the correction for a slightly thick girdle thickness (which is medium – slightly thick on the demo report), the new estimated weight is 1.01 carats, which is the same weight stated on the report.

I cover girdle thickness and corrections further down the page.

Weight Estimation Formula For Oval Cut Diamonds

The weight estimation formula for Oval Cut Diamonds is very similar to that of Round Brilliants as you:

  • (Length + Width/2)¬≤ x Depth x 0.0062

So you want to find the average diameter of the Diamond, which is adding the length and width together and then divide this by 2, then multiply that figure by itself and then by the depth of the stone and then the adjustment figure for Oval Cut Diamonds.

Weight Estimation Formula For Emerald, Pear, Marquise and Radiant Cut Diamonds

Doing weight estimation for these styles of cut requires finding the length-to-width ratio of the stone, which fortunately is very easy to do as you simply divide the length of Diamond by the width.

For example, a 9x7mm Emerald Cut Diamond has a length-to-width ratio of 1.28 : 1, once you have figured out the ratio, you then use the adjustment factor with the ratio closest to that of your stone in the formula, which is:

  • Length x Width x Depth x Adjustment Factor

Each of these styles of cut has its own adjustment factors, which I’ve listed in the tables below:

Emerald Cut Diamonds

Length to Width RatioAdjustment Factor
1 : 10.0080
1.5 : 10.0092
2.0 : 10.0100
2.5 : 10.0106

In my calculator, I’ve used the 1.5 : 1 ratio as this is the most common ratio that I have come across with Emerald Cut Diamonds.

Pear Cut Diamonds

Length to Width RatioAdjustment Factor
1.25 : 10.0061
1.5 : 10.0060
2.0 : 10.0057

I’ve used the 1.5 : 1 adjustment factor in my calculator.

Marquise Cut Diamonds

Marquise Cut Diamond
Length to Width RatioAdjustment Factor
1.5 : 10.00565
2.0 : 10.00580
2.5 : 10.00585
3.0 : 10.00595

I’ve used the 2.0 : 1 adjustment factor in my calculator.

Radiant Cut Diamonds

Radiant Cut Diamond
Length to Width RatioAdjustment Factor
1 : 10.0081
1.5 : 10.0084

I’ve used the 1.5 : 1 ratio in my calculator.

Weight Estimation Formula For Other Styles Of Cut

The weight estimation formulas for all the other styles of cut I’ve included in my calculator, such as Princess, Cushion and Heart are a bit simpler to use as they don’t require any additional calculations as the formula is:

  • Length x Width x Depth x Adjustment Factor

And I’ve listed all the adjustment factors in the following table:

Style of CutAdjustment Factor
Princess Cut0.0083
Cushion Cut0.00815
Asscher Cut0.0080
Heart Cut0.0059
Baguette Cut0.00915
Trillion Cut0.0057

Girlde Thickness and Corrections

The final part of estimating the weight of a Diamond is making adjustments for girdle thickness and weight corrections.

Girdle Thickness

A thicker girdle means that the Diamond is going to weigh more, which is why I’ve added a girdle thickness option to the calculator as the adjustment figures stated are for a thin – medium girdle.

Assessing the thickness of a girdle can be challenging and to do this effectively requires training and experience, plus the style of setting can also make this difficult.

Corrections

Some styles of cut may require additional corrections, such as:

  • Up to 10% for stones with wide wings or high shoulders, such as Pear or Marquise cuts
  • Up to 18% for stones with pavilion bulges such as Emerald or Radiant cuts
  • Up to 2% for stones with a large culet

Once again, as with assessing girdle thickness, this takes training and experience to do this affectively.