EMF Calculator
Choose standard conditions or the Nernst equation. For standard conditions, enter the standard reduction potentials of the cathode and anode half-reactions. For the Nernst equation, also enter temperature, moles of electrons transferred, and the reaction quotient Q.
Last updated: September 26, 2026
Frequently asked questions
What does EMF mean here?
Electromotive force (EMF) is the maximum theoretical voltage, or cell potential, that a galvanic cell can produce. Under standard conditions it's written E°cell.
Why do I enter reduction potentials for both electrodes?
By convention, standard electrode potential tables list reduction potentials. The formula E°cell = E°(cathode) − E°(anode) is built to use reduction potentials directly for both half-reactions - you should not flip the sign of the anode value first.
What does a positive or negative E°cell mean?
A positive E°cell means the reaction as written is thermodynamically favorable under standard conditions. A negative value means the reverse reaction is favorable instead.
What is the Nernst equation used for?
It adjusts the cell potential for conditions that aren't standard - specifically, a reaction quotient Q different from 1 and a temperature that may differ from 298.15 K (25 °C).
Why does Q = 0 give an error?
The Nernst equation includes ln(Q), and the natural logarithm of zero is undefined (it approaches negative infinity), so the calculator can't return a finite potential in that case.
Does this calculator help me build a battery?
No. It's strictly an educational calculation of theoretical cell potential from the values you provide. It doesn't cover electrode materials, electrolyte preparation, or cell construction.