Methods for calculating a self-bias on a substrate in a process chamber may include measuring a DC potential of a substrate disposed on a substrate support of a process chamber while providing a bias power from a power source to a cathode at a first frequency; measuring a voltage, current and phase shift at a matching network coupled to the power source while providing the bias power; calculating an effective impedance of the cathode by determining a linear relationship between a calculated voltage and the measured DC potential of the substrate; calculating a first linear coefficient and a second linear coefficient of the linear relationship between the calculated voltage and the measured DC potential of the substrate; and calculating a self bias on the substrate by utilizing the first linear coefficient, second linear coefficient, measured DC potential of the substrate, effective impedance, and measured phase shift.