Abstract A model is proposed for the gravity flow of particles that is particularly applicable to cohesive powders. The flow criterion is first estimated by describing the distribution of solids pressure within a vessel and by calculating the ‘flowability’ of a cylindrical block above the aperture. A flow rate equation is derived from a dynamic force balance on the block which gives an acceleration and a velocity profile in the discharging block. The seemingly steady flow is in fact a rapidly fluctuating one as the loading switches from one state to another. Computed results from the model explain several well known phenomena in particle discharge from hoppers and the method described gives a clear basis for design.