Providing coverage in closed environments becomes very crucial more and more. This is due to the great importance it gains nowadays as many indoor environments, such as factories, airports, large malls, and even indoor theme parks are deployed throughout the world. Internal base transceiver stations (BTSs) can be deployed to do so. Using internal BTSs can ensure permanent access albeit from inside buildings. In this paper, the author aims to reach a precise path loss estimation in closed environments (Indoor environments). This would significantly help the operators and cellular network designers due to the important role it is expected to play in determining appropriate cell size; that is a cell size with acceptable performance, which leads to achieve reasonable overall system cost. Matlab was used to realize the aforementioned goal. The path loss has been estimated in many possible indoor scenarios, which facilitates selection of appropriate cell size. The cell size may vary according to the required signal-to-noise ratio (SNRreq)........... Keywords: ..........wireless channel characteristics, attenuation and dispersion, large-scale fading, small-scale fading, path loss predicting models