The development of infrared Focal Plane Array (FPA) detectors in format size is a process from sparseness to density and from smallness to largeness. It is limited by the factors such as material growth of large area detectors and fabrication of small pixels. Strategic FPAs are usually used to detect point source targets while tactical FPAs are usually used to detect extended source targets. Starting from the related basic concepts, the evolution of FPA format is analyzed and the relationship between the operation range and the FPA format is discussed. Since TV formats are changeless, the further increase trend of the tactical FPAs in format will be either stopped or slower after their full frame formats are realized. On the other hand, the larger the format of the FPA is, the wider area it can cover each time is. So, the strategic FPAs will develop toward super-large format.