A model is proposed that describes the yield locus of powders. The model is based on the adhesive contact of elastic spheres theory developed by Johnson, Kendall, and Roberts (JKR model). The proposed model improves the results by applying the Warren Spring Laboratory (WSL) equation and the Coulomb model. Only two parameters are needed in the present model to describe the yield locus of a powder: powder cohesion (C) and the coefficient of friction (mu) of the powder bed. The study verifies the validity of the new equation to describe the yield locus of different powders. The proposed model was used to calculate the cohesion and coefficient of friction of monomodal quartz particle beds with different average particle sizes. The study examines the influence of average particle size (d(s)) and bed compactness (phi) on these parameters. Cohesion was observed to increase by the sixth power of compactness and inverse of the particle Sauter diameter. The bed coefficient of friction increased asymptotically with bed compactness, this relationship depending on particle size. (C) 2011 Elsevier Ltd. All rights reserved.