The common cuckoo is 32–34 centimetres long from bill to tail (with a tail of 13–15 centimetres and a wingspan of 55–60 centimetres. The legs are short. It is greyish with a slender body and long tail and can be mistaken for a falcon in flight, where the wingbeats are regular. During the breeding season, common cuckoos often settle on an open perch with drooped wings and raised tail. There is a rufous colour morph, which occurs occasionally in adult females but more often in juveniles.