How to Measure the Points & Carats of Diamonds

Diamonds are evaluated using what the jewelry industry calls the "four C's"--color, cut, clarity and carat weight. You may have to be a jeweler to accurately assess the first three, but all you need to determine carat-weight is a good scale capable of measuring to the milligram. When measuring diamonds, 1 carat is equal to 200 milligrams, or two-tenths of a gram. Each carat is divided into 100 "points" of 2 milligrams apiece. So a 75-point diamond is 0.75 carats, or 150 milligrams.

Instructions

1

Find a scale capable of measuring milligrams. These are often referred to as milligram scales, gem scales or jewelry scales. See the Tips below for more information.

2

Remove the diamond from any setting. You can't accurately measure a diamond while it's set.

3

Calibrate the scale. The weights involved here are so small, a scale that's just a little "off" could give you a highly inaccurate reading. Instructions for calibration should be included with the scale; some even come with metal blocks of precise weights to aid in calibration.

4

Place the diamond on the scale and read the weight.

5

Do the math. Subtract 200 milligrams for each carat. Take the remainder and divide it by 2 for the remaining points. For example, if a diamond weighs in at 320 milligrams--lucky you--that's 1 carat (200 milligrams) and 60 points (120 milligrams divided by two), or 1.6 carats.

6

Take the diamond off the scale and repeat the process, starting with Step 3. Twenty milligrams is exceedingly small--less than 1/100th the weight of a dime--so the more times you calibrate and measure, the more confident you can be about the weight.