ABSTRACT This article explores the politics of scale-making in infrastructural development. It argues that ‘megaprojects’, rather than self-evidently ‘big’, are constructed and contested across a continuity of scales from the ‘global’ to the microscopic. Scalar struggles are constitutive of the projects as well as of their contestation. I examine this through a focus on a disputed high-speed railway project in Alpine Italy. First, I examine expert contests over ‘big numbers’ describing the project. Here, the ‘bigness’ is discussed on its own terms, but its rationality is disputed. Second, I study a campaign by local mayors who challenge the project by stressing infrastructural needs that could be met in their respective towns for a fraction of the railway's cost. Third, I describe controversies over microscopic pathogens released during railway construction. This highlights how the megaprojects’ apparent ‘bigness’ depends on the ability to obviate socio-material relations and actants at other scales.