Thickness of a material can be calculated by measuring energy loss through the matter if the stopping power of the material is well known. This method is widely used to measure energy degrader, backing and target thickness for nuclear reaction experiments. However, the ions continuously lose their energy as they move through the matter, and also stopping power changes because of its energy dependent nature. For this reason, when calculating the thickness, one must take into account this effect, especially for a thick material. ThiMeT code takes into account stopping power changes through matter and calculates the accurate thickness by using SRIM. ThiMeT code also can be used for the determination of the required thickness for energy degraders. An experimental method for thickness measurement and calculation with ThiMeT code will be presented.