A mathematical equation, namely Jouyban–Acree model, for calculating apparent acid dissociation constants (pK a ) in hydro-organic mixtures with respect to the concentration of organic solvent and temperature is proposed. The correlation ability of the model is evaluated by employing pK a values of 17 different acids in water–cosolvent systems. The results show that the model is able to correlate the pK a values with an overall average percentage differences (APD) of 1.71±1.86%. In order to test the prediction capability of the model, nine experimental pK a values from each data set have been employed to train the model, then the pK a values at other solvent compositions and temperatures were predicted and the overall APD obtained is 2.10±2.42%. The applicability of the extended form of Jouyban–Acree model on pK a data of analytes in ternary solvent mixtures is also shown.