The penis typically stops growing between ages 16 and 18, once puberty is complete. Growth continues gradually throughout the teenage years, with the most significant changes happening between ages 11 and 16. Some individuals may see minor growth continue until around age 18 or 19, depending on when they entered puberty and how quickly they progressed through it.
How Growth Progresses During Puberty
Penile growth follows a predictable pattern tied to puberty’s stages. Before puberty, growth is minimal. A large study of boys from birth to age 18 found that average stretched length increased slowly from about 4.1 cm at birth to 5.4 cm at age 10. After that, growth accelerated sharply, reaching 8.2 cm by age 15 and 10.2 cm by age 18. That jump between ages 10 and 15 is when most of the change happens.
Doctors track puberty using a five-stage scale. For boys, the first sign of puberty is testicular enlargement, which usually begins between ages 9 and 14. Penile length and girth increase most during stages 3 and 4, typically between ages 12 and 16. By stage 5, the final stage, growth is essentially complete. Most boys reach this stage by 16 or 17, though late bloomers may not finish until 18 or occasionally a bit later.
The timing of puberty onset matters. A boy who starts puberty at 10 will likely finish growing earlier than one who starts at 14. This is why there’s so much variation among teenagers of the same age, and why comparing yourself to peers during adolescence gives a misleading picture of where you’ll end up.
What Drives Penile Growth
Testosterone is the primary hormone responsible for penile growth. During puberty, the brain signals the testes to ramp up testosterone production, which triggers growth in both length and girth. The tissue of the penis contains receptors that respond to testosterone, and this interaction is what drives enlargement.
Interestingly, the groundwork for penile development is laid much earlier. During fetal development, testosterone levels spike between weeks 8 and 24 of gestation, with the highest levels occurring around weeks 14 to 16. This prenatal hormone exposure shapes the initial formation of the genitalia and may influence adult size. The sensitivity of androgen receptors, which is genetically determined, also plays a role in how effectively the body uses testosterone for growth.
Genetics is the single biggest factor in determining final size. Variations between ethnic groups and between individuals within the same ethnic group are largely explained by genetic differences and differences in the hormonal environment during fetal development. Nutrition, overall health during childhood, and conditions that affect hormone levels can also influence outcomes, but genetics sets the range.
Does Growth Continue After Puberty?
Once puberty ends, the penis does not continue to grow. There is no second growth phase in the 20s or 30s. Products, supplements, exercises, and devices that claim to increase size in adults have been widely studied, and the Urology Care Foundation has found that almost none are effective.
That said, perceived size can change. Weight gain adds fat to the pubic area, which can make the penis appear shorter. Weight loss can reverse this effect. Erection quality also fluctuates with age, cardiovascular health, and other factors, which can affect how large the penis appears when erect without any actual change in tissue size.
What’s Actually Average
Concerns about size are extremely common, but most men significantly underestimate how they compare. A 2025 meta-analysis pooling data from tens of thousands of men found the following averages: erect length of 13.84 cm (about 5.5 inches), flaccid length of 9.22 cm (about 3.6 inches), and erect circumference of 11.91 cm (about 4.7 inches). These are measured from the pubic bone to the tip, pressing the ruler into the fat pad above the penis to get a consistent reading.
There’s a wide range of normal. The clinical threshold for a condition called micropenis, which is a specific medical diagnosis, is a stretched length under 7.5 cm (about 3 inches) in adults. This is rare and is typically identified in childhood, not adulthood. If you’re above that threshold, you fall within the normal range regardless of where you land relative to the average.
When Size Concerns Become a Problem
It’s normal for teenagers and young men to wonder about size, especially during puberty when bodies are changing at different rates. But for some men, this concern becomes consuming. A condition called penile dysmorphic disorder describes men who are preoccupied with the size or shape of their penis to a degree that causes significant shame or interferes with daily life, even when their measurements are objectively normal. This is a form of body dysmorphic disorder, and it responds well to psychological treatment.
Research comparing men who sought clinical help for size concerns found that the majority had penises within the normal range. The issue was perception, not anatomy. If thoughts about size are affecting your relationships, sexual confidence, or mental health, that’s a pattern worth addressing with a therapist rather than with products or procedures.