The long-eared owl is a medium-sized owl, which measures between in total length. Their wingspan is relatively large for their size, measuring . However, compared to other widespread owls considered of medium size and to which they can appear broadly similar in size, such as barn owl ("Tyto alba"), short-eared owls and tawny owls ("Strix aluco"), the long-eared owl is quite a bit lighter and slenderer bodied, with mature weights around half of those of tawny owls not being uncommon. As expected in owls and birds of prey in general, long-eared owls display reverse sexual dimorphism in which females are usually slightly larger than males (to the contrary of most non-raptorial birds). Males furthermore may tend to be somewhat paler in plumage than females. In Finland, one survey of the body mass of mature birds found that 22 males averaged while 20 females averaged . In body mass, European long-eared owls per a study were shown to run contrary to Bergmann's rule (that widespread animals should be smaller closer to the Equator) as body mass seemed to increase further south, being lightest in Sweden, where 37 males averaged and 24 females averaged , intermediate in Denmark and heaviest in the Netherlands, where 21 males averaged and 24 females averaged . In migratory owls largely from Scandinavian summer grounds in England, the average weight of 8 males was and the average of 28 females was . Meanwhile, in various studies in North America, 38 males (in Montana) were found to average , 55 males (also Montana in a different study) to average and 15 males (from Idaho) . From the same studies, respectively, 28 females averaged , 49 females averaged and 19 females averaged . Museum specimens in North America were found to average in 38 males and in 28 females, while 520 migrating adults in Duluth, Minnesota averaged . In all, long-eared owl males may vary in weight from while females may vary from .