An analytical solution is derived to predict the axial solid transport in rotary kilns. With it the local depth of the solid bed can be calculated conveniently in dependence on the kiln geometry (diameter and length). the operational variables of the kiln (rotation speed, feed rate and inclination), the property of the material (angle of repose) and the height of the discharge dam. The depth profile of the solid bed is found to depend only on three dimensionless variables. Comparisons demonstrate that the deviation of the analytical result from the numerical result is negligibly small. Good agreement was found between the analytical solution and measured values. (C) 2008 Elsevier Ltd. All rights reserved.