Abstract: Metallic membranes under lateral pressure are widely used to protect equipments from the danger of overpressure or to accomplish some particular switch operation. The membranes are required to be ruptured at the prescribed pressure. Due to shortage of appropriate calculating methods, the determination of ultimate load has to severely depend on experiments. Two approximate analytical solutions are investigated for the influences of both curvature and thickness upon the stresses at the crown of membranes, and a semi-empirical method is put forward to estimate the ultimate pressure. Comparing with the experimental results of many kinds of metal sheets with 86 to 910 of span-to-thickness ratios including aluminum, copper, nickel and stainless steel, the relative errors of calculated ultimate pressure by this method, by and large, do not exceed 5.0%, and the mean relative error is 2.07%.