About the Standard Cell Potential Calculator
This standard cell potential calculator finds the voltage of a galvanic (voltaic) or electrolytic cell under standard conditions. Choose the reduction half-reaction at the cathode and the one reversed at the anode from 39 common couples, and it returns E°cell = E°cathode − E°anode, whether the reaction is spontaneous, the number of electrons transferred, the standard Gibbs energy change and the equilibrium constant.
Standard reduction potentials are taken from Appendix L of OpenStax Chemistry 2e, measured against the standard hydrogen electrode at 25 °C, 1 M solutes and 1 bar gases. Classic set-ups such as the Daniell cell (zinc–copper), the lead–acid battery (PbO₂/PbSO₄ couples) and silver–copper displacement are all covered, and a custom option lets you type any potential from your own table.
Remember that you never multiply E° values by stoichiometric coefficients — potential is an intensive property. Coefficients matter only for n, which the calculator takes as the least common multiple of the electrons in each half-reaction. For non-standard concentrations, use the Nernst equation.
With the default inputs, the standard cell potential e°cell is 1.0988 V. Change any value above to recalculate instantly.
How to use the standard cell potential calculator
- 1Choose the half-reaction that is reduced (the cathode).
- 2Choose the half-reaction that is oxidised (the anode), as its reduction potential is listed.
- 3Use Custom to enter a potential from your own table.
- 4Read E°cell — positive means spontaneous — plus n, ΔG° and K.
Formula and method
Both electrodes are described by their standard reduction potentials. Reduction happens at the cathode and oxidation at the anode, so the cell potential is the cathode potential minus the anode potential (equivalently, the reduction potential plus the oxidation potential of the reversed anode reaction). A positive E°cell means the reaction is spontaneous under standard conditions.
The standard Gibbs energy is ΔG° = −nFE°, with F = 96,485.33 C/mol and n the electrons transferred in the balanced overall reaction (the least common multiple of the two half-reactions). The equilibrium constant follows from ΔG° = −RT ln K at 298.15 K.
- E°
- Standard reduction potential vs SHE (V)
- n
- Moles of electrons transferred per mole of reaction
- F
- Faraday constant, 96,485.33 C/mol
- R, T
- Gas constant 8.314 J/(mol·K) and 298.15 K
Worked examples
Daniell cell: Zn | Zn²⁺ || Cu²⁺ | Cu
Copper is reduced (+0.337 V) and zinc is oxidised (−0.7618 V). E°cell = 0.337 − (−0.7618) = 1.0988 V. With n = 2, ΔG° = −2 × 96,485 × 1.0988 = −212.0 kJ/mol and K ≈ 1.4 × 10³⁷.
Silver and copper (different electron counts)
2Ag⁺ + Cu → 2Ag + Cu²⁺. E°cell = 0.7996 − 0.337 = 0.4626 V — the silver potential is not doubled even though two silver ions are reduced. n = 2, so ΔG° = −2 × 96,485 × 0.4626 ≈ −89.3 kJ/mol.
Reversed: copper anode, zinc cathode
Trying to reduce Zn²⁺ with copper metal gives E°cell = −0.7618 − 0.337 = −1.0988 V. The negative value means the reaction will not happen on its own; you would need to apply more than 1.1 V.
Frequently asked questions
How do you calculate standard cell potential?+
Look up the standard reduction potentials of both half-reactions. Subtract the anode (oxidation) value from the cathode (reduction) value: E°cell = E°cathode − E°anode. Do not multiply potentials by coefficients.
How do I know which electrode is the cathode?+
In a galvanic cell the half-reaction with the more positive reduction potential is reduced at the cathode, and the other is oxidised at the anode. That choice always gives a positive E°cell.
What does a negative cell potential mean?+
A negative E°cell means the reaction as written is non-spontaneous under standard conditions (ΔG° > 0). The reverse reaction is spontaneous, or an external voltage must drive it, as in electrolysis.
Why don’t you multiply E° by the coefficients?+
Electrode potential is energy per unit charge, an intensive property. Doubling the reaction doubles both the energy and the charge, so the voltage stays the same. Coefficients do change n in ΔG° = −nFE°.
What are standard conditions for cell potential?+
All dissolved species at 1 mol/L (strictly, unit activity), gases at 1 bar, pure solids and liquids, usually at 25 °C (298.15 K), measured against the standard hydrogen electrode defined as 0 V.