The testicles produce the primary male sex hormone testosterone, as well as sperm. The average size of a man testicle is about 4 x 3 x 2 centimeters (cm) in size and is oval shaped. Most men have two testicles, also known as testes. It’s common for one of a man’s testicles to be a different size than the other testicle. Testicles reside in the scrotum, attached at each end to the spermatic cord.

Read on to learn more about testicle size.

Healthy production of testosterone and sperm can occur within a wide range of testicular volume. Some studies have suggested that larger testicles among some mammals are associated with higher testosterone levels, while smaller testicular volume is associated with decreased sperm production.

Testosterone levels can become a concern if you have a condition such as Klinefelter syndrome, which results from having an extra X chromosome. Symptoms of this condition include smaller testes or undescended testes, and some female characteristics, such as less body and facial hair, and breast tissue growth. Having Klinefelter syndrome usually means having lower testosterone levels and reduced sperm activity. Infertility can result.

The clinical term for abnormally low testosterone is hypogonadism. Symptoms may include:

  • smaller-than-average testicles
  • breast tissue growth
  • less body or facial hair than male peers
  • other signs similar to those of Klinefelter syndrome

Hypogonadism is often treated with testosterone replacement therapy, and it can sometimes begin during puberty.

A 2013 study found that slightly smaller testicles were associated with a more nurturing quality among fathers. Reduced testosterone levels and testes volume were associated with higher levels of paternal caregiving.

If you notice swelling of your testicles, tell your doctor. Growing larger testes in adulthood can signal testicular cancer or another health problem, rather than be a sign of increasing virility.

A male’s testicle is about 1 cubic centimeter at birth and stays around that size until the testicles start growing about age 8. Then they grow steadily, reaching their adult size some time during puberty. It’s also during puberty that hair starts to grow on the scrotum and around the genitals.

Testicles tend to grow at the same rate, though one may grow slightly larger and for a little longer than the other. It’s also common for one testicle to hang a little lower than the other.

As you age, testosterone production tends to drop as your testicles start to get smaller. This is known as testicular atrophy. The change is often gradual and may not be especially noticeable. When it occurs naturally, there is no health threat. Lower testosterone levels can lead to a reduced libido and less muscle mass, but these tend to be natural parts of aging.

Certain health problems can also cause testicular atrophy, including:

Other, harmless factors can also cause temporary changes in the scrotum and testicles. Cold temperatures, in particular, can cause “shrinkage,” though this has no impact on the size of the testicles themselves.

When exposed to cold water or temperatures, the testicles may temporarily retract closer to the body through a mechanism called cremasteric retraction. This occurs because the testicles try to maintain a certain temperature that is ideal for sperm production. That temperature is slightly cooler than average body temperature, which is why the testicles tend to hang down away from the body. But when exposed to cold water or cold temperatures, the cremaster muscle kicks in, pulling the testicles up into the body for warmth.

It’s very common for one testicle to be slightly larger than the other. There is usually no medical or health explanation for a size difference.

However, if you notice a change in the size or shape of one or both testicles, you should tell your doctor. If one testicle starts to feel heavier or you feel a lump or a change of shape, it could be a tumor and possibly the first sign of testicular cancer. This form of cancer is often treated successfully, but an early diagnosis is critical. Testicular cancer or testicular torsion, which is a twisting of the spermatic cord that causes pain and swelling, should be evaluated and treated by a doctor soon after symptoms develop.

Regardless of the size of your testicles, you should perform monthly testicular self-examinations to check for lumps or other changes that might indicate disease. A self-exam can be done after a shower or before you get dressed in the morning.

To do a self-exam, take a minute to gently roll your testicles between your thumb and fingers to feel for any changes in their size, shape, or hardness. Doing this in front of a mirror may help you see what you’re doing. If you experience any pain during a gentle exam or you notice a suspicious lump, swelling, or other change, see your doctor soon. Such changes could suggest testicular cancer or an infection.

You may discuss changes to your testicles with your primary care physician or you can make an appointment to see a urologist. A urologist is a doctor who specializes in the health of the male reproductive system and the urinary tract. Don’t wait to see your doctor. Testicular cancer is usually treated by surgically removing the cancerous testicle, but when caught early, the other testicle is usually spared.

The health and function of your genitalia is more important than size. If you feel that your testicles are too small or you have other symptoms that concern you, like low libido, excessive breast tissue, or infertility, talk with your doctor. Testosterone therapy can often help. If sperm production is affected, there are fertility specialists who may be able to help you and your partner conceive a child.