http://news.yahoo.com/big-average-pe...103431957.html
Self-reported
Average length 5.6 inches (14.2 cm)
Average girth 4.8 inches (12.2 cm)
Smallest 1.6 inches (4 cm)
Largest 10.2 inches (26 cm)
Other characteristics (race, orientation etc.) not good indicators of size.