This is from the National Health service website in the UK
Average penis size
There are no average length figures for teenagers because people grow at different rates.
For adults, the average penis size is about 14-16cm (5.5-6.3 inches) when erect. The average girth for an erect penis is 12-13cm (4.7-5.1 inches).
A penis would only be considered unusually small if it was less than 3 inches (7.6cm) long when erect.
The measurements are based on a review of 50 studies on penis size conducted since 1942, which between them have measured 11,531 penises.
The review was carried out by Professor Kevan Wylie, a consultant in sexual medicine at the University of Sheffield.
There is large variation in the angle of an erect penis. Some erect penises point straight up, others straight down. Some have a slight bend to the left or right. There is no right shape. If you have a more significant bend in your penis that may cause you pain or difficulty having sex, see your GP. Sometimes, these can be symptoms of
Peyronie's disease.
Each penis is unique and boys develop at different ages and rates. During puberty, usually between the ages of 11 and 18, the penis and testicles develop more rapidly, although the penis doesn't stop growing until the age of 21.
Men unsatisfied
Regardless of actual size, many men are still unhappy with the size of their manhood.
Professor Wylie's report examined the results of an internet-based survey of more than 50,000 men and women, which revealed that 45% of men would like a larger penis. His report concluded that excessive concerns about penis size were higher among men with average-sized penises than men with small ones.
What women think
Professor Wylie's report also found differences between what women and men think. A much higher percentage of women (85%) were satisfied with their partner's penis size than the percentage of men (55%) who were satisfied with their own penis size.
According to Professor Wylie, the issue of attractiveness to women is complex. However, most studies suggest that penis size is much lower down the list of priorities for women than such issues as a man's personality and grooming.
Professor Wylie says: "It may come as a surprise to some young men, but most women have very little interest in the size of their penis and that's been shown in numerous studies over time."
He says research shows that when it comes to sex, women are much more interested in whether you are romantic, tender and sensitive to their needs and desires than your penis size.