ok...i answered my own question 
http://en.wikipedia.org/wiki/Penis
As a general rule, an animal's penis is proportional to its body
size, but this varies greatly between species — even between
closely related species. For example, an adult gorilla's erect
penis is about 4 cm (1.5 inches) in length; an adult chimpanzee,
significantly smaller (in body size) than a gorilla, has a penis
size about double that of the gorilla. In comparison, the human
penis is larger than that of any other primate, both proportional
to body size and in absolute terms.
While results vary across studies, the general consensus is that
the average human penis is approximately 12.7-15 cm (5-5.9 in) in
length and 12.3 cm (4.85 in) in circumference when fully erect. The
average penis size is slightly larger than the median size. Most of
these studies were done on subjects of primarily European descent.
Worldwide averages may vary.
A research project summarizing dozens of published studies
conducted by physicians of different nationalities, shows that
worldwide erect penis size averages vary between 9.6 cm (3.7 in)
and 16 cm (6.2 in). It has been suggested that this difference is
caused not only by genetics, but also by environmental factors such
as culture, diet, chemical/pollution exposure, etc.
