How much built mass does it take to support human life in cities—and does this relationship change with city size? While urban scaling laws have shown that many urban attributes vary nonlinearly with population, most current models of material demand still rely on linear per-capita assumptions. In this study, we analyze over 3,000 cities worldwide and find consistent sublinear scaling of total built mass with population, both across cities (β ≈ 0.90) and within them at the neighborhood scale (δ ≈ 0.75). This implies that larger and denser cities require less built mass per capita, revealing a form of material efficiency through agglomeration. Our theoretical framework further demonstrates that these city-level scaling patterns emerge from uneven population distributions within cities, linking intra-urban inequality with aggregate urban form. These findings advance our understanding of cities as nested, self-organizing systems and have broad implications for urban forecasting, digital twins, and scale-aware planning for sustainable urban infrastructure.

Urban Scaling,BUILT MASS,material efficiency