Explosive reactive armor (ERA) is a type of add-on armor that usually consists of tiles made of two metal plates with an explosive layer in between. The ERA is placed at a certain distance from the main armor to enhance its performance. ERA design is optimized based on the required effectiveness of the tiles. Various methods of defining ERA effectiveness are described. The effectiveness parameters of the mass-flux model and its derivatives, the effect of material properties, the escape length of the jet tip precursor, the explosive layer thickness, and the edge effects are analyzed, and correlations between them are presented. Analysis results are compared with available experimental data and a very good correlation is found.