Natural Ventilation is an effective method for passive cooling, increase indoor air quality rnand minimize energy consumption of a building. Natural ventilation through rnwindow openings is an effective solution to bring air into internal spaces and rnimprove indoor environmental condition. In urban centers, where the density is high rnand local wind is reduced, the geometry of a building and its opening has a rnmassive role in natural ventilation. The current building codes and regulations of rnEthiopia miss detailed guidelines for natural ventilation. On the code and regulation rnfor windows are specified only in relation to the floor area regardless of orientation, rnheight, location and climate. Since the country has different climate zone in different rnregions, the generalized building code and standard will lead to over or under ventilated rnrooms in both scenarios creates discomfort. The study attempt to determine rnventilation-based window size for urban centers of Ethiopia on different faÃ§ade rnorientation to increase the effectiveness of natural ventilation. As wind is the main rndriving force of natural ventilation, regionalizing of Ethiopia according to wind speed rnand wind direction (secondary-Inter cardinal direction) is presented in order to rnstudy the potential of natural ventilation at different regions in the country. The rnaverage wind speed is categorized using the Beaufortâ€™s scale of wind speed. The data rnaddresses the urban centers of Ethiopia and the urban centers are selected by density. rnBoth scenarios (single side ventilation and cross-ventilation) are discussed in each rnzone. Appropriate opening size is determined, using the window orientation with rnrespect to the wind flow direction and also best and worst window orientation is rnillustrated for each zone. The study verified that, the effectiveness of natural ventilation is rnassociated with wind zone where the urban centers are located.