We present an improved method for calculating from ac susceptibility measurements the critical current densityJcand the surface shielding parameter &Dgr;Hin bulk cylindrical type‐II superconductors. As first developed by Bean, the method involves harmonic analysis of an expression for the voltage induced in a pickup coil around a specimen in an axial dc magnetic field with a small ac ripple field superimposed. Values ofJcobtained by Bean's analysis are suspect, in part because the analysis does not take account of surface shielding. Ullmaier modified Bean's calculation to remedy this defect. For simplicity he did not Fourier analyze the induced voltage, choosing instead to determineJcand &Dgr;Hby comparing experimental waveforms with his calculated voltage. This procedure permits only a qualitative indication of whether the data are consistent with the model. For generality, we have modified Ullmaier's calculation by removing the approximation that the depth of penetration of the ac field is small compared to the sample radius. The resulting expression for the induced voltageVis a complicated function ofJc, &Dgr;H, and the amplitude of the ripple fieldh0. A graphical procedure has been developed which not only extracts values ofJcand &Dgr;Hfrom plots of the amplitude of the third harmonic ofVvsh0, but also provides a check for consistency of the data with the model.