Nernst Equation Calculator

How to use the Nernst equation

1. Choose an ion equilibrium potential across a membrane, or an electrode or cell potential.
2. For an ion, choose it or enter its charge and the concentrations outside and inside the cell. For a cell, enter E°, the electrons transferred and the reaction quotient.
3. Set the temperature; the potential appears in mV or V.

Frequently asked questions

What is the formula?

For an ion: E = (RT ÷ zF) × ln([outside] ÷ [inside]). For a cell: E = E° − (RT ÷ nF) × ln Q. R is the gas constant, T the temperature in kelvin and F the Faraday constant.

What are typical values in a neuron?

At 37 °C with the built-in mammalian concentrations, K⁺ is about −90 mV, Na⁺ about +67 mV and Cl⁻ about −64 mV. Real concentrations vary between cell types.

Why does temperature matter?

RT/F grows with temperature: one tenfold concentration ratio is worth 59.2 mV at 25 °C and 61.5 mV at 37 °C for a singly charged ion.