The longest penis in the animal kingdom belongs to the blue whale - 2.4 metres (8 feet).
The longest penis relative to overall size was found in an Argentine blue-bill duck which had a remarkable 42.5 cm (17 inches) long penis. This is twice the length of the entire bird and is equivalent to a human having a 3.5 metre (12 feet) long penis.
HUMAN As far as the longest human penis, there was a claimed recording of a 14 inch penis in the 1969 book "Everything You Always Wanted to Know About Sex" by Dr. David Reuben. However this was never independently verified.
Failing that, the title goes to a New Yorker by the name of Jonah Falcon (born July 29, 1970). Falcon's penis has been reliably measured as 24.1 cm (9.5 inches) flaccid, 34.3 cm (13.5 inches) erect.