The concept of shape factor, originally for non-spherical nanoparticles, has been generalized to nanowires with non-cylindrical shapes. The new shape factor is defined as the total exterior area ratio of nanowires between non-cylindrical and cylindrical shapes in identical volumes, which equals one for cylindrical shapes and is larger than one for non-cylindrical ones. Furthermore, the shape factor has been successfully introduced in the bond-energy model, which is originally for the melting temperature of cylindrical nanowires. The predicted melting temperature on Pd and Ni nanowires by the generalized bond-energy model with shape factor are more close to computation results than the original one.