It is a medium-sized bat, slightly smaller than the common noctule. It has a length of 48 to 68 mm (head and body) and a wingspan of 260 to 330 mm. The forearm measures 38 to 47 mm and the bat's weight is 11 to 20 grams. The face, ears and wings are dark. The fur is brown, darker at the base than the tip unlike that of the common noctule which is the same colour along its length. The undersides of the arms are hairy giving it the alternative name "hairy-armed bat". The ears are short and rounded with a mushroom-shaped tragus. The wings are long and narrow.Nyctalus leisleri – Science for Nature Foundation
