Understanding Penis Size and Growth During Puberty

Penis enlargement is an important symptom of puberty. Learn the average penis size for boys ages 10 to 18, plus when you can expect a penis to start and stop growing.

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

Development happens at different rates for everyone, so some teens might wonder whether they're on track. As sexual awareness increases, concerns about penis size may deepen, particularly if all other signs of puberty (including height, body hair, and voice changes) are robust.

Indeed, between the ages of 10 and 14, when most of the growth spurts occur, teens often feel the need to compare themselves with their peers. The visible changes seen in others can quickly turn from a source of curiosity to one of anxiety.

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

Illustration of a teen boy looking at a graph for "Average Penis Size for Teen Boys" on a desktop computer.

Illustration by Zoe Hansen

Stages of Puberty and Penis Development

Generally speaking, a penis will develop in a somewhat predictable pattern. According to experts at Stanford Children's Health, the stages of puberty in people with penises break down roughly as follows:

  • The onset of puberty is between 9.5 to 14 years old. The first change is often an enlargement of the testicles, and penis growth begins one year after this. The scrotum will also drop, thin, darken, and get bigger around this time.
  • Pubic hair appears at about 13.5 years old.
  • Nocturnal emissions (also known as "wet dreams") begin around 14 years.
  • Other changes (such as facial hair, a deeper voice, and acne) become apparent around 15 years old.

When Do Penises Start Growing?

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

It can be difficult to know exactly when puberty will start and how your child will develop, as there's a wide range of normal. But you might consider scheduling an appointment with their doctor if their penis hasn't started to grow after the appearance of body and facial hair. The good news is that penis size rarely correlates to medical problems. 

Age Limit for Penis Growth

The penis will continue to grow throughout puberty, but the exact timing differs for each person. The American Academy of Pediatrics (AAP) says adult-size genitals generally develop anywhere between ages 13 and 18.

Just as when penis growth begins, there's no specific age at which penis growth stops. However, generally speaking, little additional growth can be expected after ages 18-21.

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:

 Age  Penis Length
10 to 11  1.6 to 3.1 inches
12  2.0 to 4.0 inches
13  2.0 to 4.7 inches
14   2.4 to 5.5 inches
15  3.1 to 5.9 inches
16  3.9 to 5.9 inches
17  3.9 to 6.3 inches
18   4.3 to 6.7 inches

Again, you should take these numbers with a grain of salt, 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 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. Penis size doesn't influence sexual function or other aspects of development.

Measuring Penis Size

Because there may be errors in how the penis is measured, it's usually best to have it done by a pediatrician or, better yet, an adolescent health specialist. That said, the penis is typically measured from the base to the tip of the penis. When stretched, the penis reaches a similar size as when erect.

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. 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.

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.

Diagnosis of an Abnormal Penis Size

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.

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.

Keep in mind that there may be other factors that explain a penis' abnormally short appearance, such as 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.

Embracing the Size of Your Penis

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.

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.

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Sources
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