In accordance to the implementation of Indonesia broadband plan as well as to evaluate the spectrum used for mobile broadband, an assessment of spectrum requirement is needed to acquire the spectrum estimation. This research presents Indonesia system (INS) model, an empirical model to estimate spectrum requirement for mobile broadband in Indonesia. This model is derived by elaborating a reference ITU model specified in ITU-R Recommendation M.1768-1 and an empirical Federal Communications Commission (FCC) model. This paper also presents the results of using the three models within a simplified ITU model scenario. The comparison of the results between the three models shows that the INS model deliver similar pattern of results with FCC model in dense urban and urban regions, while it shows similar pattern of results with ITU Model in suburban and rural region. It is found from the results that additional 840 MHz will be required in 2025 based on ITU model, while based on INS model, Indonesia need 295 MHz.