There are different methods for the determining particle sizes which  depends on size. İf you are using coarse particles, you can be used the Sieve analysiz with different sieve sizes. On the other hand, if you are using fine or nano powders, you should be used Laser diffraction method. It should be noted that Laser diffraction method is widely used by reaserchers. 

A particle size of powder that has not fall within a nano size range can easily be determined by the use of a standard iso-sieves with apertures of known micron sizes. The powder is poured on the sieves and vibrate for at least 15 minutes, and the required sizes are sorted out by the one retained on a particular size aperture as +....microns and the one that passed through as -....microns. However, for a nano particle size (X 10 -9) a laser diffraction method that utilizes powerful rays for size differentiation will be more adequate.