An in situ method has been developed for the determination of real active surface area of electrodes through the charge required for monolayer coverage of the electrode surface by overpotential deposited hydrogen (OPD H), i.e., Q(OPD,H), by means of simple discharging (OPD H desorption) following galvanostatic charging (OPD H adsorption), experiments. The procedure requires simple equipment and easy subsequent data treatment. Surface area measurements on platinum and stainless steel 304 electrodes in 5M KOH aqueous solutions obtained by this method are consistent with those from ac impedance spectroscopy.