The effect of frictional properties on cavity formation was studied. Until now, most of the researchers have proposed various correlations to predict the cavity size neglecting the effect of stresses on cavity formation. In the present study, the effect of stresses has been considered along with pressure and bed weight terms. These three forces are expressed in mathematical form and solved analytically for one-dimensional case using a force balance approach. Based on the force balance, the cavity size is predicted. Results have been compared with the experimental and published data of two-dimensional model. An excellent agreement is found. The effect of void fraction, angle of friction, velocity, etc. on the cavity size has been studied. The proposed theory is applicable to any packed bed systems. Internal angle of friction between the particles and void fraction in the bed plays an important role in the prediction of cavity size. (C) 2003 Elsevier B.V. All rights reserved.