Analysis of an explosive volcanic eruption requires a knowledge of the rate of fall of ejected debris. Terminal velocities have been determined experimentally for pumice of various grain‐sizes and also for lithic fragments and sanidine crystals from two series of volcanic eruptions. Theoretical terminal velocities for cylinders and rough and smooth spheres of various grain‐sizes and densities have been computed. The results for cylinders agree very closely with the corresponding experimentally measured values. Computed terminal velocities for particles with various diameters, densities and shapes are presented graphically.