The presence of surface energy has an important effect on the physical and mechanical performance of nanoscale structures and materials. Determining the value of surface energy density has raised great concern in surface science. Especially, how to estimate the surface energy density of curved and even stochastically rough surfaces remains unsolved. The present paper is aimed to investigate the surface energy density of rough metal surfaces by atomistic calculations. The surface energy densities of periodic sinusoidal surfaces and stochastically rough surfaces are calculated. Simulation results suggest an analytical model to determine the surface energy density of rough surfaces by the surface geometric parameters and the surface energy density of planar surface.