Enter all but one of the concentrations and charge of each ion into the calculator to determine the ionic strength.

Ionic Strength Formula

The following formula is used to calculate the ionic strength:

I = 0.5 * ∑(c_i * z_i^2)</div>


  • I is the ionic strength
  • c_i is the concentration of the ith ion
  • z_i is the charge of the ith ion

To calculate the ionic strength, multiply the concentration of each ion by the square of its charge. Sum up the results for all ions, and multiply the sum by 0.5.

What is an Ionic Strength?

Ionic strength is a measure used in chemistry to quantify the concentration of ions in a solution. It is denoted by the symbol ‘I’ and is calculated by summing the product of the concentration of each ion (in moles per liter) and the square of its charge number. The concept of ionic strength is important because it influences several properties of a solution, such as the solubility of salts, the pH, and the speed of chemical reactions. It is particularly significant in solutions with high concentrations of ions, such as seawater or mineral-rich groundwater, where it can affect the behavior of the ions and their interactions with other substances.

How to Calculate Ionic Strength?

The following steps outline how to calculate the Ionic Strength:

  1. First, determine the concentration of each ion in the solution (in mol/L).
  2. Next, determine the charge of each ion.
  3. Next, square the charge of each ion.
  4. Next, multiply the concentration of each ion by the square of its charge.
  5. Next, sum up the products obtained in the previous step.
  6. Finally, divide the sum by 2 to calculate the Ionic Strength.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Concentration of ion A (mol/L) = 0.5

Charge of ion A = +2

Concentration of ion B (mol/L) = 0.3

Charge of ion B = -1

Concentration of ion C (mol/L) = 0.2

Charge of ion C = +3

Concentration of ion D (mol/L) = 0.4

Charge of ion D = -2