Using the relation between the unperturbed dimensions parameter on one hand and the intrinsic viscosity and the statistical segment length of the polymers on the other, as predicted by the two-parameters theory, we have modified Han's equation [Polymer, 20 (1979) 1083], which is derived from the blob theory. According to the proposed equation, plotting [eta]/M-1/2 versus M3 nu -1.5, where nu is the exclude volume index, we obtain straight lines from the slopes of which we calculate the statistical segment length of flexible polymers. The value of nu is obtained from the value of the exponent of the Mark-Houwink-Sakurada equation. The proposed method is useful in the high molecular mass region in which the Stockmayer-Fixman-Burchard equation is not valid.