AbstractThe usual particle size analysis gives data on particle size distribution by weight or by values of a function related to it, e.g., the surface area of particles of the same weight. There are three methods for the determination of particle size in the sub‐sieve range Measuring the settling velocity, assuming Stokes' law. Counting particles of the same weight. Measuring the size of the observed or projected images of the particles in their most stable positions. The results gained by two of these methods have been compared, e.g., by Andreasen,2 by Bishop4 and by Jones,14 but it seems that hitherto no attempt has been made to compare systematically the results of all three, methods. This comparison, originally used merely for verifying purposes, has led to a method of measuring the mean particle shape. This measurement is executed in the following way: a fraction of hearly equal‐sized particles is isolated, their mean volume determined by the counting of particles of the same weight and the mean of their greatest cross sections (i.e., of the images of the particles in their most stable positions) is measured. The mean thickness is then calculated as a quotient of the mean volume and mean cross section, a prismoidal form of the particles being assumed.