The value of the nose‐on back scattering cross section of a semi‐infinite cone is determined by the exact methods of electromagnetic and acoustical theory, and by physical optics. It is shown that, to the degree of approximation used, the electromagnetic value and the physical‐optics value are equal. The acoustical value is found to be less than the electromagnetic value by a factor which depends only on the cone angle; both are proportional to the square of the wavelength. It is shown that the electromagnetic and physical‐optics answers agree with experimental data to within a factor of two. The electromagnetic theory results obtained hold for the cases in which the half‐cone angle is close either to 0 or to &pgr;/2.