Last Updated on 18/07/2022 by Above Diamond

What is Carat Weight of a Diamond: How to Buy?


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You might have heard that when we weigh diamonds, we use the unit “carat” and points”, or “carat” and “satang” in Thai.

Carat is one of the 4Cs of diamond that is excellent at determining the value of a diamond because the heavier the diamond carat is, the higher the value. And in most cases, a solitaire engagement ring cost is mostly dependent on the diamond itself.

But do you know how diamond stores measure their diamond carats? And what does the word “carat” actually mean? Today, we will be sharing the answer with you.

What Is a Diamond “Carat”?

carat weight
A diamond carat is a unit of weight used for weighing diamonds, 1 carat is equal to 200 milligrams or 0.2 grams.

But you should also know that the carat of a diamond does not refer to the size or the density of the diamond in any way, it just means the weight of the diamond itself.

I am saying this because different types of gems have different densities, meaning that a 1 carat diamond may not be larger than other gems that weigh the same.

Read more: Our 2020 buying guide to 1 carat diamonds

Carat vs. Points (Satang)

When we buy diamonds from a jewelry store, the staff will commonly tell us the weight of the diamond using both the carat and points (satang) units. Do you know the difference between these two units?

Distinguishing them is very easy.

As I have said, 1 carat is equal to 200 milligrams or 0.2 grams.

The satang unit is the same as the Thai baht currency (THB) , it is equal to 1/100 of a carat. In milligrams, one satang is equal to only 2 milligrams. You can also think of it as cents on the dollar.

And so when weighing diamonds, the staff will weigh the diamonds in milligrams, and then calculate the weight into the carat and satang unit.

How to Calculate a Diamond’s Carat

If you want to try calculating the carat of a diamond, we will have to use a bit of mathematics. The simplest and most popular method is to weigh the diamond in milligrams and then divide the weight by 0.2. The answer is equal to the diamond’s weight in carat.

For example, if the diamond weights at 0.1 gram or 100 milligrams, once it is divided by 0.2 it will equal 0.5. This means that the diamond is equal to half a carat.

Determining a Diamond’s Carat Weight by Measuring

If you do not have an accurate gram scale with you, making you unable to calculate the diamond carat by yourself – we have another method you could use. You could estimate the carat weight by measuring the size and diameter of the diamond which are divided by the shape of the diamond, both round diamonds and square diamonds.

Read more: 12 fancy cut diamonds and the secret techniques to buy them!

Estimating the Carat Weight of a Round Diamond

Estimating the Carat Weight of a Round Diamond
If the diamond is round in shape, you can use the following formula:

Diamond Carat = diameter (mm) x diameter (mm) x depth (mm) x 0.006

The explanation of each values are as follows:

  • The diameter of a round diamond can be measured in a straight line across the center of a diamond from one periphery point to another using the millimeters unit.
  • The depth (or the total height) is the vertical distance from the top surface of the diamond to the lowest point of the diamond.
  • For example, if your diamond is round and has a diameter of 4mm and a depth of 2 mm, the calculator is as follows.
  • Diamond Carat = diameter (mm) x diameter (mm) x depth (mm) x 0.006
  • 0.2 carats = 4 x 4 x 2 x 0.006

Estimating a Fancy Square-Shaped Diamond’s Carat Weight by Measuring

princess cut diamond
Whether your diamond is square or rectangular, you are able to use the formula below. The diamonds that this formula can be used on include but are not limited to the emerald cut, the asscher cut or the princess cut.

Diamond Carat = Length x Width x Depth x Coefficient

Each value is explained as follows:

  • The length and the width is measured from the outer edge of the diamond.
  • The depth is measured with the same method as the round shaped diamond, that is, measuring the distance from the top surface of the diamond to the lowest point of the diamond.

The coefficient depends on the ratio between the length and the width of the diamond, the approximate values are below:

  • Length / Width 1.25, so the coefficient is 0.0080
  • Length / Width 1.50, so the coefficient is 0.0090
  • Length / Width 2.00, so the coefficient is 0.0100
  • Length / Width 2.50, so the coefficient is 0.0105

And if the length to width ratio of your diamond is not the exact same as these numbers, you can use the closest number.

For example, if your diamond is square in shape and has a depth of 2.5 mm, a length of 5 mm and a width of 3.5 mm, the length to width ratio will be 5/3.5 = 1.43

The closest number to 1.43 is 1.50 and so you can use the coefficient 0.0090

Once we are done with that, we will calculate the carat next. The calculations are as follows:

  • Diamond Carat = Length x Width x Depth x Coefficient
  • 5 x 3.5 x 2.5 x 0.0090 = 0.394 carats, or about 39 satang (points).

However, keep in mind that this method is only suitable when you only need a rough estimate of the diamond’s carat. If you need to know the precise values, it is better to use a scale.

carat weight

Steps to Measure the Diamond’s Carat

If you bring your diamond to a diamond store and wants to have it weigh, the steps are usually as follows

1. Place the Diamond Onto the Scale
The scale used should be sensitive enough to measure up to the milligrams unit, if your diamond is already set onto a ring – it is necessary to have it removed from the ring by a technician to measure its carat.
2. Weigh the Diamond in Grams or Milligrams
Use a scale that can measure in both grams and milligrams, if the scale measures in grams it must also state the decimals accurately. Once done, write down the numbers.
3. Calculate the Diamond’s Carat
If the measurement is in milligrams, divide it by 200. If the measurement is in grams, divide it by 0.2
4. Calculate the Diamond’s Satang
Once done, bring the decimals from the carat measurement and multiply it by 100, the sum is the diamond’s weight in satang.
5. Know How to Use the Carat and Satang Unit
For example, if your diamond weighs 1.35 carats, it can also be called 1 carat and 35 satang. This is useful for you to know as some diamond store’s staff will be using this unit.


That is it. Now you are able to confidently walk into a diamond store, fully knowing the process of weighing a diamond. Knowing this enables you to receive better quality diamonds with a price tag that is suitable to the carat weight you want your diamond to have. If you are looking for diamonds with good color grades and reasonable price tags, you can come in for a consultation at Above Diamond to ensure that you will receive a precious diamond that your heart desires.

Browse our selection of certified diamonds: HERE

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