Solids friction factor is a parameter required for predicting the pressure drop in a process of pneumatic conveying. It depends upon a number of non-dimensional parameters. In this paper, experimental data for a 2. m long section of a 173. m long pipeline has been used to develop a mathematical model for solids friction factor. The model predicts the pressure drop with a low error margin for the 2. m long pipeline. Although the model has been developed for a 2. m long straight pipeline with fly ash as the conveying material, it has also been scaled-up for a 173. m long straight pipeline. By scaling-up, the predicted pressure drop lies within an acceptable error margin. Since the model seems to be having less dependence upon the parameter of particle density, it predicts the pressure drop with less error margin for the experimental data of other conveying materials such as alumina and cement. The model shows high error in predicting pressure drop for the experimental data for a different pipeline configuration. © 2015 Elsevier B.V.