Methods for determining particle size are a constituent part of substance classification and are very helpful in determination of substance properties and finaly their purpose. Since technology advanced in the last few decades there are various methods for determining particle size. Some of them are sedimentation, laser diffraction, acoustic methods, light scattering and electrical sensing. Each method has certain advantages and disadvantages in its application so their development went according to it. The most popular method for determining particle size today is laser diffraction. It is characterized by wide application, simple performance, speed and also the possibility to analize wide range of particle sizes and disperzions. On the other hand, determining particle size with acoustic spectroscopy is interesting because it separates absorption from scattering which is very hard to accomplish with other methods. With this method it is possible to determine particle size in colloids and slurries. The technique consists of propagating ultrasonic waves of a range of frequencies through the particulate system and accurately measuring the attenuation at each frequency. This attenuation spectrum can be converted to a particle size distribution and a measure of the concentration of the dispersed phase.