We develop a numerical and an analytical approach to estimate the persistence length l(p) and mean-square end-to-end distance (R-2) of complex semiflexible polymers. Numerically, l(p) and (R2) are determined by averaging a large set of single chain conformations with the correct dihedral angle distributions p(rho i). Analytically, 11, and (R-2) are extracted from the tangent tangent correlation function. We apply both approaches to two semiflexible conjugated polymers, poly(3-hexylthiophene) (P3HT) and poly((9,9-dioctylfluorene)-2,7-diyl-a/t44,7-bis(thiophen-5-y1)-2,1,3-benzothiadiazole]-2',2"- diy1) (PFTBT). Results obtained via the two methods agree for polymers with any degree of polymerization N. Our methods can be applied to any serniflexible polymers with any number of distinct moieties.