Assuming that the concentration is at equilibrium  and the flow velocity is zero, meaning that only the ion species moves, the Nernst–Planck equation takes the form:
Rather than a general electric field, if we assume that only the electrostatic component is significant, the equation is further simplified by removing the time derivative of the magnetic vector potential:
Finally, in units of mol/(m·s) and the gas constant , one obtains the more familiar form:
where  is the Faraday constant equal to ; the product of Avogadro constant and the elementary charge.