A means of assessing the requirements of a filter from the filter response specification. The steepness factor A_S for a low-pass filter response is given by the ratio f_S/f_c, where f_S is the frequency having the minimum required stop-band attenuation and f_c is the cut-off frequency of the pass-band. Once the steepness factor is calculated from the required filter response, it is compared with published normalized filter curves and a design is selected that meets or exceeds the requirements.