Estimation of the metastable zone width has been explored by using models based on the fact that metastable zone width is determined by the nucleation mechanisms acting within a crystallizer. Calculations were carried out for three organic systems and 28 aqueous inorganic systems at the various cooling rates and compositions. Both seeded and unseeded systems have also been applied to the calculations. The models developed were verified with published experimental data. About 150-data points of metastable zone widths measured from bench-scale crystallizer were compared To those obtained by the model. Theoretical model could be used for the prediction of metastable zone width for various nucleation processes.