Equilibrium Constant Calculator
Choose to calculate K from equilibrium concentrations and stoichiometric coefficients, or from a standard Gibbs free-energy change ΔG° using ΔG° = −RT ln K.
Last updated: September 26, 2026
Frequently asked questions
What is an equilibrium constant?
It's a number, K, that describes the ratio of products to reactants (each raised to its stoichiometric coefficient) at chemical equilibrium for a given reaction and temperature.
Why are K values sometimes labeled Kc or Kp?
Kc traditionally denotes an equilibrium constant expressed with molar concentrations, and Kp with partial pressures for gas-phase reactions. This calculator works generically with whatever equilibrium values you enter.
How do I calculate K from ΔG°?
Use the relationship ΔG° = −RT ln K, rearranged to K = exp(−ΔG°/RT). This calculator's second mode does that conversion directly, with temperature in kelvin.
Why does the calculator call the equilibrium constant dimensionless?
Strictly, the thermodynamic equilibrium constant is dimensionless because it uses activities relative to a defined standard state. In practice, chemists often use raw concentrations or pressures as an approximation, which works well for dilute or ideal systems but less well for concentrated or nonideal ones.
How is this different from the Gibbs Free Energy Calculator?
The Gibbs Free Energy Calculator computes ΔG from ΔH, ΔS, and T. This calculator instead computes an equilibrium constant, either from equilibrium concentrations directly, or from a ΔG° value you already have.
Does this account for nonideal solutions?
Not directly. Real solutions deviate from ideal behavior at higher concentrations. The Activity Coefficient Calculator estimates a correction factor for that, using the Debye-Hückel limiting law for dilute ionic solutions.