The inherent factors influencing the shear strength of particulate materials are also believed to influence the flow rate through a hopper. These inherent particle characteristics include particle size, particle-size distribution, particle shape, angularity, hardness, and surface roughness. To determine the effect of inherent particle characteristics on flow rate and pluviated void ratio, a wide range of materials were tested. These materials ranged from manufactured sands and glass beads to natural sands. Determination of particle size, particle-size distribution, and hardness was achieved by conducting conventional tests such as sieve analyses and specific gravity tests. Quantification of the shape and angularity parameter is more difficult due to the nonavailability of any standard techniques. To achieve the objective of quantifying shape and angularity, a new technique was developed utilizing the image analyzer. Two shape parameters, namely, Shape Factor and Angularity Factor, were determined for various materials. Shape and Angularity Factors were correlated with flow rate as well as the pluviated void ratio. Overall, the results indicate that as shape and angularity of particles increase, the flow rate decreases, and pluviated void ratio increase. A good correlation between drained shear strength properties and the flow rates measured in the cone was also found to exist. Therefore, index tests such as flow rate through a flow cone (hopper) can be used to estimate the drained monotonic strength of particulate materials. (C) 2003 Elsevier B.V. All rights reserved.