Nernst Equilibrium Potential Calculator
Compute the equilibrium (Nernst) potential of an ion across a cell membrane at body temperature from its charge and the outside/inside concentrations.
How to Use the Nernst Equilibrium Potential Calculator
- Enter the ion charge (1 for Na⁺/K⁺, 2 for Ca²⁺, −1 for Cl⁻).
- Enter the extracellular and intracellular concentrations.
- Enter the temperature in °C (reference).
- Click Calculate.
Use Cases
- •Neuroscience and physiology courses.
- •Patch-clamp experiment interpretation.
- •Teaching membrane biophysics.
Formula
E = (R·T / z·F) · ln(C_out / C_in). At 37 °C this reduces to E (mV) = (61.5 / z) · log10(C_out / C_in).
Frequently Asked Questions
Which ions should I try?
Mammalian neuron: K⁺ in 140, out 5 → −89 mV; Na⁺ in 15, out 145 → +61 mV; Cl⁻ in 10, out 110 → −64 mV; Ca²⁺ in 0.0001, out 2 → +130 mV.
Why 61.5 at 37 °C?
61.5 mV = RT ln10 / F at 310 K. At 25 °C the constant is 59.2 mV, at 20 °C it is 58.2 mV.
What about the Goldman equation?
Nernst gives the equilibrium for one ion. Multiple-ion resting potentials require the Goldman-Hodgkin-Katz equation with permeability ratios.