Understanding Penis Size and Growth During Puberty

Adolescence is a time for growth spurts and other changes caused by the onset of puberty. In teen boys, the testicles get bigger, the scrotum begins to enlarge and look different, and the penis grows in size.

As sexual awareness increases, some teens might wonder whether their penis size is normal. Researchers say the average erect penis length is 5.1 to 5.5 inches, though you should take these numbers with a grain of salt, understanding that everyone develops at a different rate.

Knowing what to expect—and what an "average" penis size really means—can help teens navigate the uncertainty of puberty. Keep reading to learn about normal penis development, whether there's an age limit for penis growth, and other common concerns.

Average Penis Size by Age

The average penis size by age was outlined in Adolescent and Young Adult Health Care: A Practical Guide by Lawrence Neinstein, MD. These guidelines shouldn't be used to check whether a teen is developing "on schedule" (an action that may underscore insecurity). Rather, you can refer to them if your child fears they're falling behind in relation to all other markers for puberty.

Here are the approximate size ranges by age for a non-erect penis:

Again, you shouldn't take these numbers as complete truth, as guidelines tend to vary. One large study of more than 15,000 adult participants found a mean flaccid penis length of 9.16 centimeters (3.61 inches), which is smaller than the average penis ranges listed above.

Erect penis length is typically a few inches longer than the non-erect size; the study mentioned above found an average length of 5.1 inches for an erect penis.

When Do Penises Start Growing?

The penis generally starts enlarging between 9.5 to 14 years old. It should happen around one year after the testicles begin growing. Your child's penis will grow in length and then in width.

Unlike wet dreams and acne, penis growth isn't associated with a particular age, so this is just an estimated range. The timeline will vary depending on many factors, including genetics, environmental influences, and the onset of puberty.

Consider scheduling an appointment with your child's doctor if their penis hasn't started to grow after the appearance of body and facial hair.

Age Limit for Penis Growth

Just as when penis growth begins, there's no specific age at which penis growth stops. The American Academy of Pediatrics (AAP) says adult-size genitals usually develop anywhere between ages 13 and 18. Generally speaking, little additional growth can be expected after ages 18-21, though everyone is different.

Is My Penis Size Too Small?

The diagnosis of an abnormally small penis would seem to be a pretty straightforward process, but it's not. While a physical exam may establish that a penis is below what's expected for a child's age, it can't accurately predict how much growth may still occur.

Factors that explain a penis' abnormally short appearance include the following:

• Excessive pelvic or suprapubic fat can obscure an otherwise normal-sized penis.
• If the child has a large frame, it may create the impression that the penis is smaller than it is.
• Less commonly, congenital conditions can limit how much of the penis is externally seen. Examples include penoscrotal webbing (in which the scrotum extends up the underside of the penis, creating an indistinct junction between the two) and phimosis (in which the foreskin is unable to retract).
• Small penis size can sometimes occur as a result of a genetic disorder (such as Klinefelter's syndrome) that impedes the production of testosterone during fetal development.

What Is a Micropenis?

By definition, a "micropenis" measures 2.5 deviations smaller than the mean average for someone's age. Early diagnosis—usually in infancy or early childhood—can lead to effective treatment. If hormone deficiency is the underlying cause, for example, hormone supplementation can be effective at encouraging catch-up growth.

Does Penis Size Matter?

According to research, only 55% of adult men are satisfied with their penis length, even though the vast majority of their partners (85%) report being satisfied.

Concerns about penis size may be understandable in teens going through puberty. Ultimately, penis size should never be considered a measurement of one's masculinity or virility. These cultural attitudes only serve to undermine teens' confidence at a time when they are only just starting to explore who they are.

Penis size doesn't influence sexual function or other aspects of development. It also doesn't correlate to medical problems most of the time.

Can You Increase Penis Size? 

To treat a micropenis, research suggests that testosterone replacement therapy (TRT) is most effective in infancy and early childhood (before the onset of puberty). TRT may increase the child's penis size to the reference range for their age. Any TRT should be done with caution, be aligned with fertility goals, and managed by endocrinology and/or urology specialists.

For older boys, surgery may be explored to treat concealed penis abnormalities. The approach can vary, but it may include circumcision or more extensive reconstructive procedures in which the skin of the penis is "degloved" and repositioned with sutures and skin grafts.

Penis enlargement surgery (phalloplasty) is not considered a reasonable option until later in life. The risk of complications may outweigh the perceived benefits, and the results tend to be variable at best, so phalloplasty isn't a decision to take lightly.

How to Talk to a Teen About Penis Size

As their penis starts growing during puberty, many kids will wonder how it measures up. They may worry whether their penis is normal or too small—and this concern is common among adults as well.

Your child may or may not bring up their worries with you. Either way, here are some tips for addressing the topic.

• Talk about puberty development in a general way, letting your child know you're open to any questions.
• Give them information on what's normal and share that it's common for people to feel their penis is too small—even if it's well within the average range.
• Reassure them that their penis will look smaller when non-erect and in colder temperatures.
• Refer to your pediatrician for additional information on penis size. If your child has concerns, the doctor can assess if their penis is developing as expected and/or answer any questions they may have. By allowing an objective third party into the conversation, you can avoid any suggestion that there's a "problem" that needs resolving.