What is the standard cell potential formula?

E°cell = E°cathode − E°anode, where both values are standard reduction potentials. The cathode is where reduction (gain of electrons) occurs; the anode is where oxidation (loss of electrons) occurs.

Why do we subtract, not add, the anode potential?

Standard reduction potentials are always tabulated as reduction half-reactions. At the anode, the reaction is reversed (oxidation), which negates the potential. Subtracting E°anode is equivalent to adding the standard oxidation potential of the anode.

How do I find the number of electrons transferred (n)?

Balance the two half-reactions so the electrons cancel. For example, Zn → Zn²⁺ + 2e⁻ (anode) and Cu²⁺ + 2e⁻ → Cu (cathode) both transfer n = 2 electrons. If the electron counts differ, multiply each half-reaction to equalize.

What does a negative E°cell mean?

A negative E°cell means the reaction as written is non-spontaneous under standard conditions (ΔG° > 0). Reversing the cell direction (swapping cathode and anode) would make it spontaneous. Electrolytic cells deliberately drive non-spontaneous reactions using external voltage.

What are standard conditions?

Standard conditions are 25 °C (298.15 K), 1 M concentration for all aqueous species, and 1 atm partial pressure for all gases. Real cells deviate from E°cell; use the Nernst equation for non-standard concentrations.

What is Faraday's constant?

Faraday's constant F = 96,485 C/mol is the charge of one mole of electrons. It appears in ΔG° = −nFE°, linking cell potential to thermodynamic free energy.

Standard Cell Potential Calculator

Calculate the standard cell potential (E°cell) by entering cathode and anode reduction potentials, or pick from 30+ common half-reactions.

Half-Reaction Inputs

Cathode (reduction) half-reaction E°_cathode (V)

Anode (oxidation) half-reaction E°_anode (V, as reduction potential)

Electrons transferred (n)

Needed to compute ΔG°.

Enter cathode and anode potentials,
then click Calculate.

Copied!

Summary

This calculator applies the standard cell potential formula E°cell = E°cathode − E°anode to determine the voltage of an electrochemical cell under standard conditions (25 °C, 1 M, 1 atm). It also computes the Gibbs free energy change (ΔG° = −nFE°) and tells you whether the cell reaction is spontaneous. You can type reduction potentials manually or choose from a table of over 40 common half-reactions.

How it works

Select or type the cathode (reduction) half-reaction and its standard reduction potential (E°) in volts.
Select or type the anode (oxidation) half-reaction and its standard reduction potential in volts.
The calculator computes E°cell = E°cathode − E°anode.
Enter the number of electrons transferred (n) to get ΔG° = −nFE° in kJ/mol.
A positive E°cell indicates a spontaneous (galvanic) cell; a negative value means non-spontaneous.

Use cases

Determine the voltage of a zinc-copper galvanic (Daniell) cell.
Check whether a proposed electrochemical reaction is spontaneous.
Calculate ΔG° for redox reactions in thermodynamics coursework.
Design electrolytic cells and verify minimum voltage requirements.
Solve AP Chemistry and university electrochemistry exam problems.
Compare different electrode combinations for battery design.
Verify half-reaction potential values against a reference table.
Explore the relationship between cell potential and free energy.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu

Standard Cell Potential Calculator

Half-Reaction Inputs

Calculation Breakdown

Gibbs Free Energy

Summary

How it works

Use cases

Frequently Asked Questions

Standard Cell Potential Calculator

Use the Standard Cell Potential Calculator

Half-Reaction Inputs

Calculation Breakdown

Gibbs Free Energy

Summary

How it works

Use cases

Frequently Asked Questions