The Nernst equation can be used to calculate the equilibrium potential for an ion based on its charge (valence) and its concentration on each side of a membrane. This voltage is often referred to as the Nernst potential or the reversal potential. This potential is determined using the concentration of the ion both inside and outside the membrane.

When the membrane is in thermodynamic equilibrium (i.e., no net flux of ions), and if the cell is permeable to only one ion, then the membrane potential must be equal to the Nernst potential for that ion.