Faraday constant, F

The charge carried by one mole of electrons. It converts between an amount of electrons and a quantity of charge, which makes it the bridge between chemistry and electricity in every electrochemical calculation.

F = 96,485.33212… C/mol

Exact, derived. The decimal runs on past ten significant figures, so it is cut off there and marked …, the way NIST prints it, rather than rounded.

In other units

Faraday constant in SI units and in other units
Quantity	Value
F	96,485.33212… C/mol
F	96.48533212… kJ/(V·mol)
F	26.80148114… A·h/mol

F in kJ/(V·mol)

96,485.33212… C/mol
= 96,485.33212… J/(V·mol)
= 96,485.33212… J/(V·mol) ÷ 1000 J/kJ
= 96.48533212… kJ/(V·mol)

A coulomb times a volt is a joule, so this is the form ΔG° = −nFE° wants for an answer in kJ/mol.

F in A·h/mol

96,485.33212… A·s/mol ÷ 3600 s/h
= 26.80148114… A·h/mol

The charge in a mole of electrons as a battery capacity.

Where the value comes from

F is the Avogadro constant times the elementary charge: the number of electrons in a mole times the charge on each. Both have been exact since 2019, so F is exact too.

Its decimal does end, but only after eighteen significant figures, at 96,485.3321233100184 C/mol, so every printed value is cut short somewhere.

Michael Faraday’s laws of electrolysis, from the 1830s, are where the name comes from: the mass a current deposits is proportional to the charge passed, and F is the charge that deposits a mole of a singly charged ion.

F from the Avogadro constant and e

F = N_A × e
= 6.02214076 × 10²³ × 1.602176634 × 10⁻¹⁹
= 96,485.33212… C/mol

Which form to use

For converting between charge and moles of electrons, 96,485 C/mol is enough for most work. The common rounding to 96,500 is 0.015 percent high.

For free energy from a cell potential, ΔG° = −nFE°, use 96.485 kJ/(V·mol) and the answer comes out in kJ/mol directly.

In the Nernst equation F appears as RT/F, which is 25.69 mV at 25 °C. Multiplied by ln 10 it becomes 59.16 mV, the shift in potential for each tenfold change in concentration in a one-electron reaction.

Common mistakes

Forgetting n, the number of electrons transferred. Depositing a mole of copper from Cu²⁺ takes 2F, not F.
Mixing joules and kilojoules in ΔG° = −nFE°. With F in C/mol and E° in volts the result is in J/mol.
Rounding F to 96,500 and then quoting a result to five figures.

Tools that use it

Resting Membrane Potential Simulator uses it in RT/F, which scales the Nernst and Goldman equations.
Galvanic Cell Simulator turns the current into moles of electrons, and so into the mass each electrode loses or gains.
Nernst Equation Calculator turns a cell potential into free energy, ΔG° = −nFE°, and into K through RT/nF.

Related constants

Avogadro constant, N_A = 6.02214076 × 10²³ mol⁻¹
Elementary charge, e = 1.602176634 × 10⁻¹⁹ C
Molar gas constant, R = 8.31446261815324 J/(mol·K)