Each ion has an equilibrium potential associated with it whereby the diffusive forces and the electrical forces balance. This is given by the Nernst Equation
where T is the absolute temperature , is the ideal gas constant, is Faraday's constant, and z is the valence of the ion. Generally people use the logarithm base 10 in which case the Nernst equation is multiplied by the factor 2.303. At just multiply the logarithm base 10 of the ratio of outside to inside by 58 mV to get the equilibrium potential. At the multiplication factor is just 62 mV. The table at the end of this section shows the typical equilibrium potentials for various membranes at various temperatures.