The central area of a megacity, which features high-intensity development, large population density, and concentrated urban functions, demonstrates the most prominent urban problems. Addressing the urban malaise in megacities necessitates analyzing and demonstrating the reasonable scale of the megacity central area. This study proposes that commuting time is the core controlling factor determining the reasonable scale of the megacity central area. Combining with point of interest data of multi-type land use and the geographic information system data for street administrative division, we identified the current central urban areas of ten cities in China using big data analysis and the clustering method; their current traffic efficiencies were then evaluated based on path navigation data via web maps and mobile phone signaling data verification. Finally, demonstration results were presented through quantitative analysis. Our study shows that the current central areas of the ten megacities cannot satisfy residents' need for a proper commuting time; considering factors such as technological development and improvement in the level of governance, 13 ‒ 15 km is the upper limit of equivalent radius for the central area of a megacity.