A blank shape determining method includes: a process of making a forming analysis of forming a reference blank into a reference formed product and a acquiring sheet thickness distribution and a plastic strain distribution; a process of acquiring a forming failure evaluation index for the reference blank; a process of estimating a region, which includes an end edge portion at which the forming failure evaluation index exceeds a predetermined threshold, within the reference blank as a forming failure region; a process of generating a plurality of corrected blanks; a process of making a forming analysis of forming the corrected blanks into corrected formed products and acquiring a sheet thickness distribution and a plastic strain distribution; a process of acquiring the forming failure evaluation index for the corrected formed product; and a process of determining a shape of the corrected blank having a smallest maximum value of the forming failure evaluation index as a shape of a blank provided for press forming.