The Nernst equation is one of the most important equations in electrochemistry. To calculate the cell potential at non-standard-state conditions, the equation is E = E' - (2.303 * RT / nF) * log10(Q), where E is the potential in volts, E' is the standard potential in volts, R is the gas constant, T is the temperature in kelvins, n is the number of moles of electrons transferred, F is the Faraday constant, and Q is the reaction quotient. At standard temperature (25°C or 298 K), the equation has the form E = E' - (0.0592 / n) * log(Q). The reaction quotient has the usual form [products] / [reactants].
A table of standard reduction potentials gives the voltage at standard conditions (1.00 M for all solutions and 1.00 atm for all gases). The Nernst equation allows for the calculation of the cell potential E at other conditions of concentration and pressure.