Are larger firms more productive, more scalable, or both? We use firm-level panel data from thirteen countries and employ a broad set of methods to estimate factor elasticities–capturing returns to scale (RTS)–and total factor productivity (TFP). We f ind substantial RTS heterogeneity within industries, with larger firms exhibiting higher RTS driven by greater intermediate input elasticities. TFP, by contrast, rises with firm size only up to the top decile before declining. Incorporating RTS heterogeneity into a standard model of entrepreneurship more than doubles the efficiency losses from financial frictions compared with a conventional calibration with only TFP differences.