When Does a Penis Stop Growing?

A penis starts growing rapidly between ages 10 and 14 and generally slows down and stops growing by ages 16 to 21 when puberty ends. The timeline depends largely on when puberty starts, which may be influenced by genetics, nutrition, obesity, and other factors.

As such, a boy who thinks he has a small penis may eventually catch up or have a larger penis than his peer. Conversely, a boy who experiences early puberty may or may not achieve the same growth as his peers by the time he reaches his early 20s. Ultimately, penis growth and its adult shape and size vary widely.

Penis Growth and Puberty

The growth of the penis actually starts well before puberty during "mini-puberty." This stage of development occurs during the first six months of life. The growth of the penis and testicles during mini-puberty is often predictive of how large they will be in later life. Most of the growth happens between the second and third months of life.

Thereafter, the penis will grow more or less in relationship to the boy's size until puberty.

With the onset of puberty, typically starting between ages 10 and 14, the size of the penis will quickly increase. The greatest growth spurt tends to occur between ages 12 and 15, with length of the penis generally increasing before the girth (circumference).

Other changes can occur in tandem with the increase in penis size. Boys will start to get taller and more muscular, grow facial and pubic hair, and develop an Adam's apple. Frequent erections, ejaculation, and nocturnal emissions ("wet dreams") are also characteristic.

Between the ages of 16 and 18, penis growth will slow down and eventually stop as puberty ends. With that said, some individuals may experience continued growth into their early 20s, albeit minimal.

Why Penis Growth Occurs

In males, penis growth is directed by male sex hormones known as androgens. The main androgen called testosterone is produced by the testicles and converted by the body into the more active form known as dihydrotestosterone (DHT).

During puberty (and mini-puberty), DHT stimulates growth by attaching to androgen receptors in the penis. At the end of puberty, the number of androgen receptors quickly decreases, coinciding with the termination of penile growth.

Puberty itself is triggered by a part of the brain called the hypothalamus which stimulates the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. The release of LH and FSH is what ultimately kickstarts the production of testosterone during puberty.

Variations in Time

The age at which a penis stops growing can vary by as many as five or more years. The factors influencing the timing include:

• Age of onset of puberty
• Genetics (which can influence the age of onset)
• Poor nutritional status (which can contribute to delays in puberty)
• Childhood obesity (which can contribute to early puberty)
• Conditions like hypothyroidism or Klinefelter syndrome that cause hypogonadism (low testosterone) and delayed puberty

Generally, early-onset puberty corresponds to a younger age when the penis stops growing. Conversely, delayed puberty tends to correspond to an older age when the penis stops growing.

But, this is not always the case. With certain conditions like Klinefelter syndrome, the decreased production of testosterone may not only delays puberty but lead to smaller penis growth irrespective of timing.

With that being said, the vast majority of males will achieve their ultimate penis size by the time they are 18 or 19. After that, the penis isn't likely to grow all that much longer or thicker.

Average Penis Size

There is no way accurately predict when puberty will start and penis growth will stop. Likewise, there is no way to accurately predict how large a penis will be after puberty.

Outside of certain family genetics, including inheritable factors like height, there is no clear-cut way to guess how large a boy's penis will eventually get.

The average size of a male penis is often smaller than many people think. According to a 2015 study published in BJU International, the average length and girth of erect and flaccid (soft) penises in a group of 15,421 healthy men were, as follows:

• Erect length: 5.3 inches (13.12 cm)
• Erect girth: 4.59 inches (11.66 cm)
• Flaccid length: 4.59 inches (11.66 cm)
• Flaccid girth: about 3.66 inches (9.31 cm)

With that said, 95% of the study participants had an average erect penis length of 6.3 inches (16 cm). The remaining 5% had an average erect penis length of 3.94 inches (10 cm).

To obtain an accurate measurement of your penis, it is best to do so with a measuring tape and a full erection, as follows:

• Length: Hold the measuring tape against your pubic bone on the top side of your penis. Measure from the base of the penis to the tip.
• Girth: Snugly wrap the measuring tape around the thickest part of your penis just below the head or around the thickest part.

Beyond curiosity value, measuring your penis correctly helps you select the right condom size to protect against unintended pregnancy and sexually transmitted infections (STIs).

Summary

A penis will rapidly increase in size at the onset of puberty, usually between ages 10 and 14, and typically stop at the end of puberty, usually between the ages of 16 and 18. However, some males may continue to experience growth into their early 20s.