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
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 Diameter² 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)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 Ratio | Adjustment Factor |
|---|---|
| 1 : 1 | 0.0080 |
| 1.5 : 1 | 0.0092 |
| 2.0 : 1 | 0.0100 |
| 2.5 : 1 | 0.0106 |
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 Ratio | Adjustment Factor |
|---|---|
| 1.25 : 1 | 0.0061 |
| 1.5 : 1 | 0.0060 |
| 2.0 : 1 | 0.0057 |
I’ve used the 1.5 : 1 adjustment factor in my calculator for Pear Cut Diamonds.
Marquise Cut Diamonds
| Length to Width Ratio | Adjustment Factor |
|---|---|
| 1.5 : 1 | 0.00565 |
| 2.0 : 1 | 0.00580 |
| 2.5 : 1 | 0.00585 |
| 3.0 : 1 | 0.00595 |
I’ve used the 2.0 : 1 adjustment factor in my calculator for Marquise Cut Diamonds.
Radiant Cut Diamonds
| Length to Width Ratio | Adjustment Factor |
|---|---|
| 1 : 1 | 0.0081 |
| 1.5 : 1 | 0.0084 |
I’ve used the 1.5 : 1 ratio in my calculator for Radiant Cut Diamonds.
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 Cut | Adjustment Factor |
|---|---|
| Princess Cut | 0.0083 |
| Cushion Cut | 0.00815 |
| Asscher Cut | 0.0080 |
| Heart Cut | 0.0059 |
| Baguette Cut | 0.00915 |
| Trillion Cut | 0.0057 |
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.