This communication correlates two empirical methods; flow in a rotating drum with flow in bench scale hoppers. The flow characteristics of 13 cohesive granular materials were studied in the gravitational displacement Rheometer (GDR) and compared to flow in hoppers of varying angle and discharge diameter at fixed temperature and moisture conditions. The GDR proved to be an effective and convenient toot for examining flow properties of pharmaceutical materials, both pure and mixtures. A flow Index obtained from GDR measurements is directly correlated to the flow through hoppers, providing a predictive method for hopper design and a convenient experimental test for screening materials and determining their suitability for specific hopper systems. Analysis of industrial scale hoppers will be addressed in future communication. (c) 2006 Elsevier Ltd. All rights reserved.