Thin films, papers, or foils produced from graphene-based materials have been the focus of considerable research interest in recent years. They have a range of applications including energy storage, selective filtration of liquids, and gas storage. For all of these applications, the critical attribute of the films is their pore volume, however there remains a considerable challenge around characterizing the accessible microscopic surface area of the material/s in their intended state of application. In this work an image processing based approach is presented for estimating the lower threshold of specific surface area for graphene based films that possess a typical multi-layered structure. Canny edge detection is used together with tortuosity measurements to construct sheet areas from layer edges. The method serves as a simple independent characterization technique. We find that our predicted specific surface area values for a range of similar films vary by less than 4x as compared to the reported values which vary by > 1.1×10³ in range.