Men everywhere worry that their penis is smaller than it should be or that it won't satisfy a lover. But research suggests that most men underestimate the size of their pride and joy.
Man has always placed great importance on the size of his penis. Many cultures associate penis size with masculinity. Throughout the ages, it has come to symbolise qualities such as virility, fertility, strength, ability and courage.
Some men go to extreme lengths to try to increase the size of their penis. Indian mystics known as Sadhus have been known to stretch their penis from an early age by hanging weights on it, while the Topinama tribesmen of Brazil encouraged poisonous snakes to bite their penis to enlarge it.
Feeling inadequate can really damage a man's self-confidence and affect his social life. It can lead to issues from being unable to use public urinals or shared shower rooms, to avoiding intimate relationships.
Companies around the world have exploited this anxiety, selling pills, penis extenders and other penis enlargement products that promise to "increase the length and girth of your manhood fast, or your money back!"
Measuring your penis
Most men's view about their penis is formed during childhood. Growing up, they may see the penis of an older brother, friend or their father and mentally compare this to their own.
Fears and anxiety about penis size may also arise after taunts from other people during adolescence or following remarks from a sexual partner.
However, men often have the wrong perspective on their penis, says sexual health expert Dr David Delvin. "When you look down at your own organ, it seems shorter than it really is," he says. "In contrast, when you glance around at other guys in changing rooms or showers, you get a sideways view of them. So they usually seem to be longer than you are."
To see your penis as other people would, look at yourself undressed in front of a full-length mirror. The penis looks longer and larger than when observed from above.
At some stage, most boys get out a ruler or a tape measure to find out how long their penis is. Dr Delvin says there's little point in doing this when the penis is limp because the length of a flaccid penis can vary a lot, for example depending on how cold the room is.
To get a precise measurement, do it when you have an erection. Take the measurement from the base of the penis on the side nearer to the tummy, up to the tip, where the hole is.
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.
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.
If you're still worried
Counselling has proven to be beneficial for men with penis anxiety. Therapy helps patients identify and correct any distorted views about their penis, build self-confidence and overcome fears about sexual relationships.
Professor Wylie says: "Therapy allows these men to overcome their anxiety about meeting a potential partner, where before they wouldn't even dare engage because of their fear."
Find out more about what a sex therapist does.
Numerous physical treatments claim to increase penis size, but there is very little evidence that these work. Find out more about penis enlargement treatments.
If you are worried about your health have a look at the Man MOT, a confidential online surgery where you can talk to a GP anonymously.