Is Penis Size Genetic?

Penis size is largely determined by your genetic makeup, but other influences come into play as well. Hormones, lifestyle, and other environmental factors can also affect penis size.

Certain lifestyle changes, such as weight loss around the base of the penis, can make it appear longer. Trimming pubic hair can also help enhance the look of your penis. Although these adjustments do not change the actual penis length, they can help you feel more confident.

Man getting results from his doctor

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Which Genes Influence Penis Size?

Penis size is dependent on a combination of genes, specifically the sex chromosomes, received from your parents. The sex chromosomes decide one’s biological sex and secondary sexual characteristics that appear during puberty such as facial hair in males and rounder hips in females.

Males have one X and one Y chromosome, while females have two X chromosomes. The Y chromosome is inherited from the father and contains the “male-determining” gene, the SRY gene. The SRY gene leads to the formation of testes and external and internal male genitalia in the embryo.

However, while the presence of the Y chromosome leads to the development of the penis, it does not necessarily determine the characteristics of the penis, such as its length and girth, or circumference. This may be more reliant on the X chromosome, which only comes from the mother and contains around 900 genes compared with the Y chromosome’s estimated 90 genes.

This influence from the X chromosome would then explain why some siblings’ penis sizes vary, since each sibling may differ in which X chromosome they received from their mother even if they have the same father.

Individual genes unique to each person (not genes from parents) can also influence penis size. Genetic mutations may contribute to penis length and appearance as well.

Other Influential Factors

A number of other factors can affect penis size, including hormones, nutrition, and exposure to toxins in the womb.

Hormones, like testosterone, particularly during puberty, affect penis growth and its final length in adulthood. Low testosterone is linked to a smaller penis size, as well as a lower libido and erectile dysfunction.

Testosterone can be raised naturally with nutrition and exercise. Nutrition, particularly in utero and in the early years of life, can affect both your hormones and overall development. Malnutrition can actually lead to smaller penis size as well.

In animal studies, exposure to toxins in the womb, such as phthalates (chemicals used to make plastic more durable), has been shown to impact penis size. Studies suggest phthalates are a type of endocrine disrupter, which can affect hormones necessary for reproduction. This link is in animal studies only and not proven in human studies.

Size Myths

There are a number of myths surrounding penis size, including:

  • Bigger feet, bigger penis: There is no correlation between a man’s shoe size and his penis size. Other body parts or features do not give clues as to how big or small a man’s penis is either. This includes the hands, facial and body hair, etc.
  • Masturbation: Masturbation does not inhibit or promote penis growth. The frequency of masturbation does not matter either.
  • Sexual satisfaction and desirability: Research has shown that penis size isn’t a relevant factor for either partner, nor does it make you necessarily more or less desirable.

Studies have shown that there may be differences in penis size based on ethnicity. However, the differences found were not large between different ethnic groups.

The most pervasive and damaging myth, however, has to be about a man’s masculinity and his penis size. Having a larger penis does not mean someone is manlier, just as a smaller penis would not make someone less manly.

The Law of Averages

The average flaccid (non-erect) penis length is 3.6 inches. When erect, the average length measured from the base of the penis to the tip is 5.2 inches. 

Despite this, most men actually overestimate the average penis length. This overestimation can lead to feelings of inadequacy, insecurity, and anxiety. Research has shown that almost half of men feel insecure about their penis size or wish it was longer.

If the size of your penis is causing you significant anxiety, understand that a longer length or larger girth is not necessarily better or manlier. Identifying unhelpful, distorted views about penis size can help you overcome these beliefs. A sex therapist can help you with this.

A Word From Verywell

While penis size is mostly determined by your genes, other factors that can affect size include hormones, nutrition, and environment. Despite what marketing may say, there are no medications or exercises that have been proven to lengthen one’s penis.

Losing excess weight and trimming pubic hair can help enhance the appearance of one’s penis. Remember that your penis, no matter its size, does not define you as a man and sexual partner.

However, while some anxiety about your penis size is absolutely normal, if it is deterring you from pursuing sexual relationships or impacting your self-esteem, do talk to a medical professional about your concerns. A sex therapist or urologist can help you work through your feelings.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Azab SS, Hamed HA, Elseginy A, Elzawahry HM, Ismail NN. Increase apparent penile length by cryolipolysis in the reduction of male suprapubic fat. Andrologia. 2021;53(3). doi:10.1111/and.13963

  2. National Human Genome Institute. Y chromosome infographic.

  3. Urology Care Foundation. What is low testosterone?

  4. Bustamante-Montes LP, Hernández-Valero MA, Flores-Pimentel D, et al. Prenatal exposure to phthalates is associated with decreased anogenital distance and penile size in male newbornsJ Dev Orig Health Dis. 2013;4(4). doi:10.1017/S2040174413000172

  5. Prause N, Park J, Leung S, Miller G. Women’s preferences for penis size: a new research method using selection among 3d modelsPLOS ONE. 2015;10(9):e0133079. doi:10.1371/journal.pone.0133079

  6. Alves Barboza R, da Silva EA, Ruellas T, Damião R. Anthropometric study of penile length in self-declared Brazilians regarding the color of the skin as White or Black: the study of a myth. Int J Impot Res. 2018;30(1):43-47. doi:10.1038/s41443-017-0009-z

  7. Weill Cornell Medicine Urology. Penis enlargement.

  8. National Health Service. Penis size.

By Molly Burford
Molly Burford is a mental health advocate and wellness book author with almost 10 years of experience in digital media.