Many of the buildings which experienced damage in recent earthquakes such as the 2015 Nepal Earthquake were reinforced concrete (RC) frame buildings with unreinforced masonry infill walls. This study proposes a simplified procedure to estimate the in-plane seismic capacity of masonry infilled RC frame buildings based on concepts of the Japanese seismic evaluation standard (JBDPA, [1]). The correlation of seismic capacity and observed damage obtained using a database of 370 existing RC frame buildings with masonry infill that experienced earthquakes in Taiwan, Ecuador and Nepal is investigated. The Is index, which represents the seismic capacity of buildings in the Japanese standard, showed good correlation with the observed damage and proved to be effective as a simple method to estimate seismic capacity. The method was then applied to 103 existing buildings in Bangladesh that have not experienced a major earthquake recently. The results emphasize the necessity for urgent seismic evaluation and retrofitting of buildings in Bangladesh.