Many males may have concerns about the size or appearance of their penis from time to time. People may wonder if penis size is genetic. We address whether this, and any other factors, play a role in determining penis size.

While it is true that people can consider penis size to be a genetic trait, many other factors impact penis size. These factors include hormones, nutrition, and diet.

In this article, we explore factors that affect penis size, average penis length, and the risks of penis enlargement methods.

three generations of males walking together who may all have a similar penis size because of geneticsShare on Pinterest
Genetics, hormones, nutrition, and diet can all affect penis size.

Genes are the building blocks that determine a living organism’s appearance and behavior. Humans inherit two copies of each gene, one from each parent. Multiple genes make up chromosomes.

Humans have 23 pairs of chromosomes. Of these, there are 22 autosomes and one set of sex chromosomes.

A person’s sex chromosomes determine their biological sex and secondary sexual characteristics.

Males inherit one Y chromosome from their male parent and one X chromosome from their female parent. Females inherit two X chromosomes, one from each parent.

The Y chromosome carries genes that oversee the development of male genitalia and fertility.

The Y chromosome determines the development of the penis and testes but not necessarily penis size or girth. These characteristics may be dependent on the X chromosome.

The X chromosone contains 900–1,400 genes, whereas the Y chromosome houses only about 70–200 genes.

This difference may explain why penis size varies among siblings with the same biological parents.

Genetic mutations may also affect penis size and appearance as well as other physical characteristics.

While quite rare, genetic conditions sometimes influence penis size include Kallmann syndrome and Klinefelter syndrome.

Thus, penis size depends on a combination of a person’s parental genes, their own unique genes, and other external factors.

The following factors also affect penis size:


Just as estrogen and progesterone affect female sexual characteristics, such as breasts, hips, and fat storage, male sex hormones, or androgens, contribute to testicular and penile growth.

During puberty, the pituitary gland produces more luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

LH promotes testosterone production in the Leydig cells of the testicles, and FSH promotes sperm production.

Variations in testosterone levels during pregnancy may cause penile abnormalities. For example, the mother may not produce enough human chorionic gonadotrophin (hCG) hormone. The hCG hormone stimulates testosterone development in the fetus.

Rare conditions, such as 5 alpha reductase deficiency and congenital adrenal hyperplasia, also affect testosterone levels and may affect genital appearance.

Even if testosterone levels are normal, some medical conditions may stop a person’s body from responding to testosterone correctly. This response is called androgen insensitivity.

When any of these hormonal issues arise, the penis of a male fetus may not develop in the usual way.


Environmental pollutants, such as pesticides, plasticizers, and other chemicals, may have a negative effect on penis size. These chemicals may act as endocrine disruptors and impact gene and hormone expression.

Epigenetics is a growing area of science investigating how the environment may affect gene expression.

Researchers believe epigenetics plays a role in development and disease. They suspect it may influence hormone function and have a role in hormone disorders.

Studies in 2015 and 2016 both suggest that prenatal exposure to chemicals, such as phthalates, negatively impacts the genital development of male newborns.

A 2019 study also suggests that epigenetic-associated dietary influences may slow genital progression in adolescent boys.


Malnutrition in the womb and throughout life may impact hormones and affect growth and development.

Furthermore, malnutrition in adolescence, as is seen in anorexia or bulimia, can delay normal puberty.

While individuals undergoing delayed puberty typically catch up eventually, symptoms of delayed puberty include a smaller penis and testicles.

Other factors

Genetics are the strongest predictors of penis size. However, factors, such as body fat and the presence or absence of pubic hair, can make the penis appear larger or smaller without affecting its true size.

When exposed to cold temperatures, the blood vessels in the penis constrict. This physiological reaction causes the penis to shrink temporarily.

Numerous myths about what factors determine penis size often lead to unnecessary stress and anxiety in people of all genders and ages. Thus, the following do not affect penis size or appearance:

  • shoe size
  • height
  • masturbation

Click here to learn more about penis size and masturbation.

The penis grows gradually after birth. However, the most significant growth occurs during puberty, or between 12-16 years of age.

Puberty usually begins in males between 9.5–14 years of age and can last up to 4years.

A penis typically reaches its maximum length and girth when a person is 18 or 19 years old. However, some people experience penile growth well into their early 20s.

Click here to learn more about when the penis starts and stops growing.

According to a 2014 review of 20 studies with a total of 15,521 males, the average penis length is:

  • 9.16 centimeters (cm) or 3.6 inches (in) when flaccid
  • 13.24 cm or 5.2 in when stretched in a flaccid state
  • 13.12 cm or 5.17 in when erect

The average penis circumference is:

  • 9.31 cm or 3.6 in when flaccid
  • 11.66 cm or 4.6 in when erect

Another 2014 article reported average erect penile dimensions based on the self-measurements obtained from 1,661 men.

The average erect penis length was 14.5 cm or 5.7 in, and the average erect penis circumference was 12.23 cm or 4.8 in.

However, as this study relied on the men’s own measurements, the results may be less reliable. The researchers deemed the results were fairly consistent with prior research.

Click here to learn more about average penis size.

The penis enlargement or male enhancement industry claims that enlargement procedures, vacuum devices, pills, and creams increase penis size.

However, there is limited research for many of these methods, and they may come with serious risks.

The majority of people seeking penis enlargement have average-sized penises, meaning that they are of adequate size for sexual activity and urination.

The Urology Care Foundation only recommends penis enhancement surgery for people with a rare condition called micropenis where a penis is two or more standard deviations below the average size.

The American Urological Association states that there is not enough high-quality evidence to support the safety or efficacy of penile augmentation surgery.

Potential risks of trying to increase penis size include:

  • swelling, infection, or scarring after surgery
  • damage due to overusing a vacuum pump or stretching devices
  • contact dermatitis that topical products may trigger
  • allergic reactions to ingredients in pills
  • erectile dysfunction

Click here to learn more about penis enlargement methods.

Genetics plays a substantial role in determining penis size. However, other factors, such as hormones, the environment, and nutrition, can affect penis size.

Other factors, including body type, physical fitness, and underlying medical conditions may affect how the penis appears and a person’s perception. However, it is important to note that most people fall into the normal range of penis sizes.

A person should speak with a doctor if they are concerned about the size or appearance of their penis.