The enduring question now has a scientific answer: 13.12 centimetres (5.16 inches) in length when erect, and 11.66 cm around, according to an analysis of more than 15,000 appendages around the world.

In a flaccid state, it found, the penis of the average Joe is all of 9.16 cm in length and has a girth of 9.31 cm.

The numbers should help "reassure the large majority of men that the size of their penis is in the normal range," said British researchers who had assembled data from studies where participants had their member measured by a professional.

The team then used the collated numbers to devise a graph that doctors can use in counselling men with "small penis anxiety".

In the worst cases, men may be diagnosed with Body Dysmorphic Disorder -- a debilitating psychological condition that can lead to obsessive and anti-social behaviour, depression and even suicide.

In reality, only 2.28 percent of the male population have an abnormally small penis, said the study -- and the same percentage an unusually large one.