在电化学中，能斯特（Nernst）方程用来计算电极上相对于标准电势（E）来说的指定氧化还原对的平衡电压（E）。能斯特方程只能在氧化还原对中两种物质同时存在时才有意义。

在常温下（25℃ = 298.15 K），有以下关系式：

因此，能斯特方程可以被简化为：

In electrochemistry, the Nernst equation is an equation that relates the reduction potential of a half-cell (or the total voltage, i.e. the electromotive force, of the full cell) at any point in time to the standard electrode potential, temperature, activity, and reaction quotient of the underlying reactions and species used. When the reaction quotient is equal to the equilibrium constant of the reaction for a given temperature, i.e. when the concentration of species are at their equilibrium values, the Nernst equation gives the equilibrium voltage of the half-cell (or the full cell), which is zero; at equilibrium, Q = K, ΔG = 0, and therefore, E = 0. It is named after the German physical chemist who first formulated it, Walther Nernst.