Penis Length
The vast majority of men measure between five and seven inches when fully erect. According to the Kinsey Institute (founded by Dr. Alfred Kinsey in 1947) the average length of an adult penis measures just less than six inches. However, the British Journal of Urology puts the average length of a penis at 5.08 inches, while the International Journal of Impotence Research puts it at 5.35 inches. A non-erect penis usually measures somewhere between 3 to 4 inches.
The current, living record holder for the longest reported penis in the world is Jonah Falcon, who can be seen in an HBO documentary called Private Dicks: Men Exposed. He measures in at 9.5 inches in length when flaccid and 13.5 inches in length when erect.
Back when the famous Kinsey Report - the first ever scientific study of real peoples’ sex lives - was initially released in 1948, Dr. Kinsey found that the smallest reported penis was 1.75 inches when erect.
A man who has an erect penis that measures less that 7 cm (or just over 2 inches) is considered to have a micro penis. The condition can usually be treated with hormone therapy or surgery.
Penis Girth
The average girth of an erect penis is between 4.7 to 5.1 inches in circumference, reports the British Journal of Urology International. How about the girth of the fella who holds the world record for longest penis? It’s a lot like grabbing at the middle of males forearm when it is flexed!
Since the majority of women’s sensitive nerve endings are concentrated near the opening of the vagina, a wider penis will have more impact (than a longer penis) on her sexual enjoyment. Why is this? Because putting more pressure on the vestibular (clitoral) bulbs –the erectile tissue next to the Clitoris and extending one on either side of the vaginal orifice - gives a woman the sense of feeling ‘filled up’ while her partner is inside her.
(Content taken from here)