When talking about jewelry and diamonds, CTW stands for Carat Total Weight but is more commonly referred to as Total Carat Weight for diamonds or gemstones (like sapphires or rubies). Total Carat Weight is the sum of the weight of all the diamonds mounted in that particular jewelry piece. It is widely used by the global jewelry trade as well as recognized diamond and gemstone certifying agencies like the Gemological Institute of America as a standard measure of weight.