In this letter, we report a useful mathematical model is proposed to predict the nucleation rate, and the Gibbs free energy of nucleation form the metastable zone width (MSZW) values measured at different cooling rate for 17 different combination of active pharmaceutical ingredients (APIs) and solvents that involves 12 different active pharmaceutical ingredients (APIs). The metastable zone width (MSZW) is crucial in crystallization processes because it defines the range of supersaturation where no spontaneous nucleation occurs, but crystal growth is possible. MSZW helps to determine the precise supersaturation levels to avoid spontaneous nucleation, which can lead to undesirable crystal sizes or polymorphs. Operating within the MSZW allows controlled crystal growth, ensuring consistent size and quality of the crystals. On the theoretical side, MSZW allows to calculate the nucleation rate which is a key factor in understanding and optimising the crystallisation. Theoretically the nucleation rate is obtained using the MSZW measured at different cooling rates using theoretical models that includes the one developed by Nyvlt, Sangwal, and Kubota . These models allow to theoretically calculate the nucleation rate kinetic constant and the order of nucleation. Moreover, these models relate the MSZW obtained at fixed saturation temperature with the rate of cooling. It will be useful to develop a theoretical model that can theoretically determine the nucleation rate at different cooling rates. Thus, to complement the established model of Nyvlt, Sangwal and Kubota, we present a new mathematical model based on the classical nucleation theory that allows to calculate nucleation rate at a fixed cooling rate based on the MSZW obtained from different starting solubility temperature. Furthermore, as the model rely on the classical nucleation theory, it immediately allows to theoretically calculate the Gibbs free energy of nucleation as a function of temperature and supersaturation at the point of nucleation. From the Gibbs free energy, it is possible to calculate the surface free energy or the interfacial tension and the radius of the critical nucleus as a function of the operating variables that mainly include the supersaturation and the temperature at which the nucleation is observed. To show the usefulness of the model and to demonstrate the fact that the model is universal, we applied the mathematical model to the experimental data on the MSZW of twelve different APIs reported at different cooling rates to obtain the nucleation rate kinetic constant, Gibbs free energy of nucleation, surface energy and the radius of nucleation as a function of supersaturation and the nucleation temperature.