Helpful information for members of the public looking to sell diamonds & diamond jewelry
Carat Weight
All other factors being equal, as the carat weight of a diamond increases, so does its value. However, this value increase is not proportionate. For example, a 3 carat diamond is not necessarily three times the value of a 1 carat with the same characteristics. Diamonds under 1 carat are portrayed in points (1 carat = 100 points). For example: a 0.90ct diamond might be referred to as 90 points. Very small diamonds, such as 1 or 2 points do not have much value as loose stones in the resale market. While they do add to the value of a jewelry piece as a whole, as loose stones, the process of removing them from jewelry and repairing any chips is more costly than the value of the diamonds themselves.

How can I determine my diamond’s carat weight?
If you have a scale which measures in grams, you can weigh your diamond and then convert that weight into carats. Here is a link to an online "gram to carat" conversion calculator.  You could also estimate its value using the millimeter chart attached below.
Diamond carat weight estimation chart: download PDF