How to Calculate a Diamond's Size by Measurements

When discussing diamonds, it's usual to think about the size. However, the size and weight of a diamond are inextricably linked. The official unit of measurement for a diamond is the carat (ct). Carat is derived from the word "carob," which is a plant seed originally used as a comparable form of measurement for a diamond. A carat is now classified as weighing 0.2 grams. You can calculate the approximate size of a diamond by its measurements, so you get some idea as to the weight in carats and therefore its approximate value. However, the cut, color and clarity of a diamond affect its exact value.

Instructions

1

Look carefully at the diamond to determine its shape. This makes a difference when you get to calculate the diamonds size by measurements. There are 10 recognized diamond shapes.

2

Use a ruler and very carefully measure the diamond across the widest point. Accuracy is important. You need a ruler that has millimetrers (mm) on the side, because the size of a diamond is measured in mm. Make a note of the measurement.

3

Visit a website that shows the measurement of diamonds and the approximate carats. Two are listed in Resources, but there are many more.

4

Scroll down or click the appropriate link to take you to a diamond chart. Look on the chart to find the shape of your diamond.

5

Compare the measurement you calculated earlier to the chart to find the same or very similar size diamond. When you find a shape and measurement comparable to your diamond, it tells you the approximate carats. You can also get an idea of the value of your diamond from the website, but to get it accurately valued, you need to take it to a diamond specialist.