This paper presents a derivation and a physical interpretation of the equal area rule (EAR) for wire-grid simulation of surfaces. We propose a new procedure that leads to a formulation for obtaining the radii for an arbitrarily meshed surface. A simple comparison of the classical EAR and the new equal area rule (NEAR) is presented in which the electric field inside a closed metallic surface, which is known to be identical to zero, is calculated using the radii predicted by the two methods. The results show that the proposed new equal area rule predicts a smaller field for the frequency range considered, suggesting an improvement over the classical EAR. © 2006 IEEE.