标准电极电势是可逆电极在标准状态及平衡态时的电势，也就是标准态时的电极电势，记作、或，上标表示标准态。标准状态意味着：溶质的有效浓度为1mol/L，气体压强为100 kPa，温度一般为298K。

虽然电池的电动势可以直接测定，但单一可逆电极的标准电极电势却只有相对值没有绝对值，而且它随着温度、浓度和压强而发生变化。电极电势的基准是标准氢电极：标准状态下H/H₂电极的电势被定为0.00V，即，其他电极电势的值在此基础上获得。当某半电池和标准氢电池电极相连时为负极，该半电池的半反应的标准电极电势为负值，且绝对值与电池电动势相等；若为正极则相反。这样求得的值称作还原电势，总反应的标准电极电势也就是两个半反应标准电极电势的差，E大于零时反应自发。

In electrochemistry, the standard electrode potential, abbreviated E° or E (with a superscript plimsoll character, pronounced "standard" or "nought"), is the measure of individual potential of a reversible electrode at standard state, which is with solutes at an effective concentration of 1 mol dm, and gases at a pressure of 1 atm. The reduction potential is an intensive property. The values are most often tabulated at 25 °C. The basis for an electrochemical cell such as the galvanic cell is always a redox reaction which can be broken down into two half-reactions: oxidation at anode (loss of electron) and reduction at cathode (gain of electron). Electricity is generated due to electric potential difference between two electrodes. This potential difference is created as a result of the difference between individual potentials of the two metal electrodes with respect to the electrolyte. (Reversible electrode is an electrode that owes its potential to changes of a reversible nature, in contrast to electrodes used in electroplating and destroyed during their use)