A pycnometer or densitometer is a device that measures the density of solids, including metal powders through measuring gas pressure using the first law of Thermodynamics and Archimedes’ principle. This device uses helium gas, because helium gas is capable of penetrating the smallest pores between the powder particles, and this in turn increases the device precision. Besides, given that helium is a perfect gas, the laws governing behaviors of perfect gas simplifies the working equations of the device. Thus, using this device, the density of any powders, sponge material and other solids can be measured.