You can calculate your diamond’s carat value by measuring it with a ruler that has millimeters on it. That’s the standard measurement for jewelry. Or you can weigh the stone if you have an accurate scale calibrated in grams and milligrams.
Definition of Carat
A carat (ct) is a measure of weight. It is exactly 200 milligrams, or .2 grams. Because it’s a measure of weight, and not of volume or size, no two carat-weighted gems will be exactly the same size. One will almost certainly have a somewhat greater density than the other. This is especially true of different types of gemstones, such as rubies, emeralds or diamonds.
Weighing Your Diamond
For this to work, you must have a very accurate scale. Weigh just the gemstone and record its weight in grams. Then divide that number by .2 to obtain the carat-weight. So, for example, if your diamond weighs .3 grams, then dividing that number by .2 would yield 1.5, or 1 ½ carats. If you don’t have access to such a scale, don’t despair. You can simply measure your diamond.
Measuring Your Diamond
All you need for this measurement is a small ruler calibrated in millimeters. If your diamond is round, simply measure the diameter of the stone, looking down on it. Let’s say it’s six millimeters. Then you measure the depth of the stone. That’s the length from the top of the stone to its pointy bottom. Let’s say it’s three millimeters.
Now multiply 6 x 6 (diameter squared) x 3 x .006. The result is .648, or about .65 of a carat. Keep in mind that this will be an approximate value.
If you have an oval ring, this will work. Just multiply the millimeters across one length of the oval and then the other one. Let’s say it’s 6mm wide and 10 mm long. Add 6 + 10 and divide by 2 (8). Then you measure the depth the same way you do for a round stone, and multiply by the same co-efficient. The depth measures 4 mm. Thus you have 8 x 8 x 4 x .006 = 1.536 carats.
Now you have a good idea of how to tell the carat-weight of your diamond, and maybe some bragging rights!