We report an electrochemical impedance spectroscopy (EIS) based method to measure the doping level of conducting polymers. Using EIS the Faradaic current and the capacitive charging current can be separated without relying on any unverifiable assumptions. We demonstrate the method for three types of conducting polymer thin films that are the basis for many commercial applications (poly(3,4-ethylenedioxythiophene), poly-3-hexylthiophene and polypyrrole). (C) 2009 Elsevier B. V. All rights reserved.