Can we just get it over with and assign one whole section to guys talking about their cocks.
...or you can measure up against this information!
http://www.calculatorslive.com/Average-Penis-Girth-Calculator.aspx
LifeStyles Condoms have conducted research into the average length and circumference of the erect penis during Spring Break in Cancun and found that the average penis length is 5.877 inches, with the majority ranging between 5.5 inches and 6.3 inches.
The average girth is 4.972 inches, with the majority ranging between 4.7 inches and 5.1 inches.
From March 11 to 17, a total 401 males over the age of 18 were measured, one at a time, by qualified medical staff (protected by gloves) in private tents at the Dady Rock nightclub in Cancun, Mexico. Of the 401 men, 300 were able to gain an erection for measurement — a success rate of only 75%.
Measurement methodology
The following criteria were enforced by a doctor and a team of four nurses, who attended each of the seven nights of the penis size research. Measuring of length was from the point at the base of the erect penis where the top of the penile shaft meets the pubic area to the tip of the glans ("head"). For uncircumcised men, the foreskin was retracted. Measuring of girth was at mid-shaft around the circumference of the penis when the penis was erect. Failure to gain an effective erection for measurement disqualified the volunteer from being included in the data for the calculation of average erect penis length and girth.
Environment
The majority of participants were U.S. college men, but it was not limited to this group. Volunteers were asked to enter a private area, where they would gain an erection and then call for the two nurses to measure their erect penis. (Male fantasy overload.) To ensure the accuracy of the data, each erect penis was measured by two of the nurses. A doctor supervised the nurses and all activity.
Volunteers tended to be groups of friends, which helped ensure a wide range of penis sizes (big and small) and provide a more accurate average figure.
Sample size
The sample included 401 male volunteers, of which only 300 were "effective" male volunteers (75 percent), because 101 volunteers (25 percent) could not gain an erection for measurement. At 300 effective measurements, the study was twice the size of any previous study that used medical staff to measure penis size. This method is more accurate and reliable than studies in which volunteers undertake self-measurement/reporting.
Yes I do know that these statistics have flaws, but it's the best I could find, without using any self reported measurements. There is a more in depth analysis of the results here.
Erect penis length
The average erect penis length was 5.877 inches (14.928 cm). Standard deviation was 0.825 inches (2.096 cm) with 54 percent of the effective sample measuring between 5.5 inches (14 cm) and 6.3 inches (16 cm).
Erect penis girth
The average erect penis girth was 4.972 inches (12.63 cm). Standard deviation was 0.508 inches (1.29 cm) or with 53.33 percent of the effective sample measuring between 4.525 inches (11.5 cm) and 5.118 inches (13 cm).
Source: Lifestyles Condom Co., 2001