Activity Coefficient Calculator
Enter the ion's charge, the solution's ionic strength, and the Debye-Hückel constant to estimate the activity coefficient γ. The limiting law is a dilute-solution model, so treat results at higher ionic strength with caution.
Last updated: September 26, 2026
Frequently asked questions
What is an activity coefficient?
An activity coefficient (γ) corrects a concentration for non-ideal behavior. Multiplying by it gives the effective concentration, or activity, that governs equilibrium in real solutions.
Which equation does this use?
The Debye-Hückel limiting law, log₁₀(γ) = −A z² √I, with a base-10 logarithm. The default A of 0.509 is the commonly quoted value for water at 25 °C.
When is the limiting law accurate?
Only for very dilute solutions, roughly ionic strength up to about 0.01 mol/kg. Beyond that, extended models such as Davies or extended Debye-Hückel equations are used, which this tool does not include.
What is ionic strength?
Ionic strength is I = ½ Σ cᵢ zᵢ², summing over all ions in solution. You supply it directly here.
Why does a higher charge lower γ so quickly?
The charge enters as z², so a divalent ion is affected four times as strongly as a monovalent ion at the same ionic strength.
Is this the same as a correlation coefficient?
No. The activity coefficient is a chemistry correction factor and has nothing to do with a statistical correlation coefficient.