Five ways into one equation.
Pick a mode below — everything recalculates live as you type, and every result shows the formula it used.
Products over reactants, using actual concentrations or pressures.
Must not equal 1 — at Q=1, E always equals E° regardless of n.
Standard potential is zero — identical electrodes, different concentrations.
Three or four inputs to an answer.
No manual required — but here's the entire flow in four moves.
Pick a mode
Cell potential is the main Nernst equation. Standard potential, Reaction quotient and Electrons each rearrange it to solve for a different unknown. Concentration cell handles the special E°=0 case.
Enter what you know
Type a number and pick its unit where one applies — volts or millivolts, kelvin, Celsius or Fahrenheit. The example chips fill everything in with one tap.
Read the result
The main answer sits up top with a useful alternate reading below it, and the exact formula with your numbers substituted sits at the bottom.
Trust the checks
Impossible inputs — a temperature at or below absolute zero, a zero or negative reaction quotient, an n of zero — get flagged with a plain-English reason instead of a wrong or broken answer. Copy any result set with one click.
One equation, five ways to use it.
Every mode above is the same relationship, just solved for a different letter.
Nernst equation
R = 8.314 J/(mol·K), F = 96485 C/mol. Relates measured potential to the standard potential and reaction quotient.
25°C simplified form
Only valid at exactly 298.15 K — this calculator uses the full RT/F term so any temperature works.
Solving for E°
Back out the standard potential from a real, measured cell voltage.
Solving for Q
Rearranges the exponent to reveal what concentration ratio produced a given voltage.
Solving for n
Useful when the number of electrons transferred in a half-reaction isn't given directly.
Concentration cell
E° = 0 because both electrodes are identical — the whole voltage comes from the concentration difference.
Questions people actually ask.
The short answers — with the long ones one tap away.
What is the Nernst equation?+
It's E = E° − (RT/nF) lnQ. It relates a cell's actual voltage (E) to its standard potential (E°), the number of electrons transferred (n), the absolute temperature (T), and the reaction quotient (Q).
What is standard electrode potential (E°)?+
E° is the cell potential measured under standard conditions: 1 M concentrations, 1 atm for gases, and usually 25°C. It's a fixed reference value looked up in standard reduction potential tables.
What is the reaction quotient Q?+
Q has the same form as the equilibrium constant expression — products over reactants — but uses actual current concentrations instead of equilibrium values. Q = 1 under standard conditions, which is why E equals E° there.
Where does the 0.0592 V constant come from?+
At 25°C (298.15 K), RT/F converted from natural log to base-10 log works out to about 0.05916 V, often rounded to 0.0592 V. That gives E = E° − (0.0592/n) log₁₀Q, valid only at 25°C.
How do you calculate a concentration cell's voltage?+
A concentration cell uses identical electrodes in solutions of different concentration, so E° = 0. Its voltage is entirely E = (RT/nF) ln(C_cathode ÷ C_anode), where the more concentrated side is the cathode.
Why does temperature affect cell potential?+
Temperature sits directly in the RT/nF term, so a hotter cell amplifies the gap between E and E° for a given reaction quotient. This calculator converts Celsius or Fahrenheit to kelvin automatically before solving.
Is this tool free, and where does my data go?+
It's completely free and runs entirely in your browser — nothing you type is uploaded, logged, or sent to any server. No account, no sign-up, no limits.