The ratio, \(\sigma \), of the root-mean-square end-to-end distance of a polymer chain with unperturbed dimensions, \(< r^{2} >_{0}^{1/2}\), to that of a freely rotating chain with the same structure, \(< r^{2} >_{0,f}^{1/2}\), i.e. \(\sqrt{\frac{< r^{2} >_{0}}{< r^{2} >_{0,f}}}\), in the limit of infinite chain length. The steric factor reflects the effect of hindrance to free rotation.