New Gem Weight Gauge. This is a new gem weight gauge. The diamond weight estimator is perfect for estimating the size of loose or mounted stones when other methods are unavailable. This estimator works for emerald, marquis, pear shaped, round and baguette stones as well as brilliant full cuts. Simply lay the gem estimator on your stone pad and place the diamond in question on the appropriate outline, and you will be able to instantly tell the approximate weight of your stone.