Re: What is the normal penis size?

Thank you for your question:

From the web site, http://www.sexualrecords.com , 

Jamison and Gebhard, (Journal for Sex Research 24: 177-183. 1988) used data 
from the Kinsey report to generate these numbers.

Flaccid penis length (mean +/- SEM: inches).......3.89 +/- 0.73
Erect penis length ...............................6.21 +/- 0.77
Flaccid penis circumference.......................3.75 +/- 0.65
Erect penis circumference.........................4.85 +/- 0.71
Erectile increase in length.......................2.30 +/- 0.71
Erectile increase in circumference................1.11 +/- 0.52

There appears to be no direct relationship between flaccid length and erect 
length.  Moreover, very small flaccid penises often reach about the same 
size when erect as large flaccid penises.

The human penis is of the vascular type. That is, there are spongy areas 
within the penis that will engorge with blood during periods of sexual 
excitment (often in 5 - 30 seconds after the onset of sexual stimulation). 
There are two cylindrical bodies along the dorsal (top) aspect of the penis  
called the corpora cavernosa (cavernous bodies) and a single corpus 
spongiosum which encirles the urethra (the tube through which urine and 
semen exit the body). Erection results when blood is trapped in these 
regions of the penis.  This is accomplished by small arteries dilating as a 
result of neural input. The increase in blood entering the penis causes an 
increased volume which passively will occlude veins carrying blood away 
adding to the engorgement.  The neurotransmitter nitric oxide is important 
in the dilation of the arteries as it ultimately stimulates the production 
of cyclic guanylyl monophosphate (cGMP) which leads to arterial dilation. 
This is the basis for the drug sildenafil's (Viagra) action {Viagra blocks 
the enzyme responsible for degrading cGMP, therefore, helps keep cGMP 
concentrations high for a longer period of time which results in the 
likelihood of erection during sexual stimulation.

The penis usually reaches final adult size during puberty. 

Penis size is often the source of much worry by men.  There seems to be a 
perception that "bigger is better".  Certainly "adult entertainment" films 
and videos feature "actors" with extarordinarly large penises, adding to 
the concern men may feel that they are too small.  Considering that the 
average vaginal size is 3 to 4 inches in length (when sexually excited) and 
2 to 2.5 inches in diameter, AND that the clitoris (equivalent to the penis 
head) is an exterior structure, most men have no problem resulting from the 
size of their penis.  

I hope this helps.

David Mallory, Ph.D.
Associate Professor of Biology
Marshall University
Huntington, WV