Standard Cell Potential Calculator
E°cell from two half-cell reduction potentials — which electrode is the cathode, the cell notation, ΔG° and the equilibrium constant — with a table of common couples.
How it works
E°cell = E°cathode − E°anode (the more positive couple is reduced); ΔG° = −n·F·E°; K = exp(n·F·E° ÷ RT)
Standard reduction potentials rank how strongly each couple pulls electrons; pairing two, the higher one runs as written (reduction, cathode) and drags the other backwards (oxidation, anode). Subtract, never add — potentials are intensive and do not scale with coefficients, though n does when converting to ΔG. A positive E° means a spontaneous reaction and a large K: every 0.059 V per electron is a factor of ten in K at 25 °C. Real cells deliver less under load and shift with concentration (Nernst).
Worked example
Daniell cell: Cu²⁺/Cu (+0.34 V) against Zn²⁺/Zn (−0.76 V): E° = 1.10 V, n = 2, ΔG° = −212 kJ/mol, K = 1.6 × 10³⁷ — zinc dissolves, copper plates out.
Frequently asked questions
Do I flip the sign of the anode potential?
No — keep both as reduction potentials and subtract the anode’s from the cathode’s. Flipping and adding gives the same number; doing both double-counts.
Why is the lithium potential so negative?
Li⁺/Li at −3.04 V is the strongest common reducing couple — the reason lithium batteries reach 3.7 V per cell.
Related calculators
For study and planning — check units and conditions against your data source before using a result in the lab.