Chlorine dissolved in water forms an equilibrium between hypochlorous acid (HOCl) & hypochlorite ions (OCl^–).  See chlorination for more details.

Hypochlorous acid is generally a much stronger disinfectant.  It is therefore important to estimate what proportion of your chlorine takes this form:

This calculator is based on equations and values from the “dissociation of hypochlorous acid” section of White’s Handbook of Chlorination¹. It is provided free of charge and without any warranty.

1 – Black & Veatch Corporation. White’s Handbook of Chlorination and Alternative Disinfectants – 5th ed (p. 74). Wiley. Kindle Edition.