Series of measurements with irregular waves were undertaken for the overtopping rate of model seawalls of vertical walls (205 cases) and of concrete block mounds placed in front of vertical walls (123 cases). Experimental data were compared and supplemented with theoretical calculations by the combination of the author's random wave breaking model in shallow waters and the weir type overflow model. The results have been compiled as twelve diagrams for the estimation of overtopping rate for two sea bottom gradients (1/10 and 1/30), three values of equivalent deepwater significant wave steepnes (0.012, 0.017, and 0.036), and two types of seawalls. The twelve diagrams enable quick estimation of the overtopping rate of seawalls at any water depth from the offshore to the foreshore.