According to Beyond the Burghal Hidage (Baker and Brooks, 2013), at any time the West Saxon fyrd could theoretically call on up to a quarter of the male population, about 125,000 people. Not all of these would have been militarised; many were occupied building fortifications, roads and bridges, and most would only have been used on a local, county level. Primarily they were deployed as burghal garrisons, which could be combined to meet threats as and when necessary.

The Burghal Hidage can give us a rough estimate of the garrisons of individual fortresses, by telling us how much land was allotted to support them. Wallingford, for example, had a garrison of roughly 2,400, Bath 1000, Exeter about 750. As to the size of battles, the Anglo-Saxon Chronicle records fairly accurately the sizes of different Viking fleets which try to raid or invade England. Fleets over 100 ships are remarkable but not extremely rare. The average longboat held a crew of around 50-55 so some Viking forces could easily have numbered 5-6,000, with later armies designed for conquest being even larger, as many as 10-20,000 men. Anglo-Saxon forces were roughly on par, if not slightly larger .