This paper presents a numerical and experimental study of the angle of repose of mono-sized coarse spheres, a most important macroscopic parameter in characterising granular materials. Numerical experiments are conducted by means of a modified discrete element method. Emphasis is given to the effects of variables related to factors such as particle characteristics, material properties and geometrical constraints. The results show that under the present simulation conditions, the angle of repose is significantly affected by the sliding and rolling frictions, particle size and container thickness, and is not sensitive to density, Poisson's ratio, damping coefficient and Young's modulus. Increasing rolling or sliding friction coefficient increases the angle of repose, while increasing particle size or container thickness decreases the angle of repose. Based on the numerical results, empirical equations are formulated for engineering application. The proposed simulation technique and equations are validated by comparing the physical and numerical experiments, where focus is given to the effects of particle size and container thickness.