Ionic Strength Calculator

About this calculator

This calculator finds the ionic strength (I) of a solution from its ions' molar concentrations and charges: I = ½·Σ(cᵢ·zᵢ²), summing over every ion, where cᵢ is concentration and zᵢ is the ion's charge. Because charge is squared, multivalent ions (like Ca²⁺ or SO₄²⁻) contribute disproportionately more to ionic strength than monovalent ones (like Na⁺ or Cl⁻) at the same concentration.

Ionic strength governs how electrostatic interactions between ions affect a solution's behavior, feeding directly into the Debye–Hückel equation for activity coefficients, which corrects ideal solution chemistry (based on concentration) to real behavior (based on activity) — essential in analytical chemistry, electrochemistry, and biochemistry, where high ionic strength buffers can shield charged biomolecules and affect enzyme activity or protein folding.

Analytical and physical chemists calculating activity coefficients, biochemists preparing buffers for protein or DNA work, and chemistry students working through Debye–Hückel problems all use this calculator, entering each ion's concentration and charge.