JayRay Projects a developer of freeware programs has just launched his free program to help calculate the carat weight of diamonds, emeralds and rubies. It is clearly useful to professional jewelers and those who collect and deal with gemstones. But anyone possessing gemstone set rings could also use this program. Just beware that the program only applies to diamonds, emeralds and rubies. Using it with other gemstones will be inaccurate as gemstone densities (mass/volume) vary.

It looks easy to use with four steps - choose gemstone, then shape and enter dimensions and click for answer.

Freewarefiles.com have yet to list a ratings value for this new program but that would likely change in the future.
http://www.freewarefiles.com/program_8_79_27353.html