Here the effect of contact properties on discrete element method (DEM) simulations of dry granular flow was investigated. The particle contact properties were first measured using particle tracking velocimetry. DEM simulations of flow from hoppers with outlet angles of 30°, 60° and 90° were then performed. The simulations were validated by comparison with experimental measurements of the flow rate from the hopper and magnetic resonance imaging (MRI) measurements of the velocities of the particles within the hopper. The mass flow rate predicted by DEM was insensitive to the contact properties used in the simulations, indicating flow rate is not a suitable parameter for validation. In contrast, the velocity of the particles in the central region of the hoppers was sensitive to the coefficients of friction. The best agreement between the simulations and the MRI measurements of the velocities of the particles was obtained using the a priori measured contact parameters.