Over the past several decades, operational forecasts of typhoon tracks have improved steadily. However, storm surge forecast skills have experienced rather modest improvements as it has been assumed to be primarily a function of maximum typhoon wind speed. In this study, numerical sensitivity experiments have been conducted for the semi-enclosed Tokyo Bay to investigate the existence of any connection between typhoon size and peak storm surge height. The radius of the maximum wind (Rmax) derived based on the 50-kt wind radius (R50) is used to define the size of a typhoon. The results show that peak storm surge height tends to increase as the size of typhoon becomes larger, which may also be supported by historical observations. Storm size plays a significant role in surge generation, particularly for very large typhoons making landfall in the upper bay. Analyses show that for a given hypothetical typhoon, the water level in the inner bay is increased by 1 m, changing Rmax from 13 km to 89 km. The findings of this study will be beneficial for the storm surge modeling community as it gives insight into the role of typhoon size, which is essential to forecast peak surge height precisely.