In the Combinatorial Substrate Epitaxy (CSE) approach, a thin film is grown at high temperature on a polycrystalline substrate. Those substrates induce a local film epitaxy on each substrate grain and an overall polycrystalline character on the macroscopic scale. Compared to single-crystalline films, this approach provides the possibility to introduce, in a controlled way, grain boundaries providing new functionalities. Therefore, controlling the microstructure and grain size of the substrates is an important step for tuning the film properties. In this paper, a complete study of the granular growth of the standard substrate material for the deposition of perovskite thin films, SrTiO3, has been carried out with different isothermal cycles highlighting the grain growth mechanisms. From these results, we are able to predict the sintering thermal cycle necessary for targeting very precisely a desired grain size and the corresponding physical properties. Indeed, highly restraint physical properties specifications are needed for advanced electronic applications. Since a classic granular growth model was used, this approach can be generalized to the broad family of oxides.