Various density functional theory (DFT) functionals and semiempirical techniques were used to predict the ionization potentials of selected conjugated polymers. Ionization potentials at infinite chain lengths were estimated using Meier fit on oligomer data. Calculated gasphase ionization potentials with BHandH functional showed good correlation with the experimental data. The results from the semiempirical techniques do not compare as favorably as the ones obtained from DFT methods. The data fitting allowed us to estimate the size of "effective ionization length'', which spanned over 20-30 double bonds in the conjugated backbone of the polymer in question.