Testicles come in many different shapes and sizes. It is also common for one testicle to be slightly larger than the other and for one testicle to hang lower. Due to this extensive variability, there are several different ways to measure a person's testicles.

One measurement looks at volume, which averages about 20 cubic centimeters (cm³). Another way to assess testicle size is to measure the length from top to bottom. On average, this length is between 4.5 and 5.1 centimeters.

People with testicles much smaller than this may worry. However, if there are no accompanying symptoms, there is rarely a problem.

Rather than comparing their testicle size with that of other people, an individual should look at whether their testicles have changed over time. Testicles that are suddenly much smaller or larger than usual may signal a problem.

In this article, we examine the potential causes of small testicles and the treatment options. We also explain when a person with small testicles should get advice from a doctor.

a young man looking pensive as he thinks about his Small testiclesShare on Pinterest
Low testosterone is one possible cause of small testicles.

A 2017 study found that testicular volume, alongside body mass index (BMI), could be a predictor of testosterone levels. On average, the participants with lower testosterone had smaller testicles.

Many people with low testosterone levels have normal sized testicles, so it is important to look at all symptoms and not just testicle size.

Some symptoms of low testosterone include:

A varicocele is an enlarged swelling of the veins within the scrotum. While some people may notice pain or swelling, others may have no symptoms at all.

Some people with varicoceles have problems with fertility. About 40% of males with infertility have varicoceles, although there are also males with varicoceles who do not have infertility.

Some individuals with a varicocele may notice that their testicles shrink or that one testicle is suddenly smaller than the other. They may also experience an aching pain deep in the scrotum.

Surgery can treat most varicoceles. In many cases, the testicles return to their usual size after surgery.

A congenital disorder is a condition that is present at birth. Some rare congenital disorders cause very small testicles.

One such disorder is Klinefelter syndrome. Klinefelter syndrome causes a male to have two or more X chromosomes instead of only one.

People with Klinefelter syndrome tend to be taller than average and have small testicles that produce little testosterone. Most people with Klinefelter syndrome are infertile.

Klinefelter syndrome can also affect brain and motor development. Children with this condition may have poor coordination or find behavioral skills challenging to learn.

During puberty, some boys with the condition develop breasts. Some people with Klinefelter syndrome get a diagnosis early in childhood, but others may be unaware that they have the condition.

Testicular atrophy is when the testicles shrink. Several conditions can cause testicular atrophy.

One well-known cause of testicular atrophy is surgery to repair an inguinal hernia. This complication is rare, affecting only about 0.5% of males who undergo primary inguinal hernia repair.

Individuals who have repeated inguinal hernia repairs have a higher risk of testicular atrophy, with about 5% developing this complication.

Some other causes of testicular atrophy include:

Little research has directly tested the link between testicle size and infertility. A 1989 study noted that out of the 1,029 infertile men in the study, 704 had normal sized testicles. The other men had differing degrees of reduction in the testicular volume of one or both testicles.

The count and movement of sperm reduced with testicle size. Men with lower testicular volume often had lower sperm production.

As most infertile men in this research study had normal sized testicles, the study did not establish a clear correlation between testicle size and fertility in those with normal sized testicles.

Men with fertility concerns should ask a doctor about testing to assess sperm quality. A doctor may also recommend blood tests to measure hormone levels.

A reduction in testicle size after testicular torsion may be a risk factor for testicular cancer. Anyone who notices that their testicles are suddenly smaller should see a doctor.

It can be difficult to distinguish the symptoms of testicular cancer from those of other types of cancer.

Some symptoms of testicular cancer include:

  • a lump on the testicles
  • an enlargement of the testicles
  • having fluid in the scrotum
  • enlarging breasts
  • a feeling of heaviness in the testicles or scrotum
  • a dull ache in the back or abdomen
  • experiencing shortness of breath

Some risk factors for testicular cancer include:

  • An undescended testicle (cryptorchidism). People with cryptorchidism are more likely to develop testicular cancer than those with descended testicles.
  • Family history. While most people with testicular cancer do not have a family history of the disease, having a first-degree relative with testicular cancer increases a person's risk.
  • HIV. People with HIV, particularly those with stage 3 HIV, have a higher chance of developing testicular cancer.
  • Previous testicular cancer. About 3–4% of those who have received a diagnosis of cancer in one testicle will develop cancer in the other testicle.
  • Race and ethnicity. White males are 4 to 5 times more likely to develop testicular cancer than black and Asian American males.
  • Age. Although testicular cancer can affect males of any age, close to 50% of testicular cancers occur in those between the ages of 20 and 34 years.

When the testicles are smaller than average, but there is no underlying medical condition, there are typically no side effects.

Medical conditions that cause small testicles can also produce other signs and symptoms. For example, a varicocele can cause pain and swelling in the scrotum.

Testicular atrophy can affect sexual and reproductive health in several ways. People may experience:

If a person is concerned about the size of their testicles and the accompanying symptoms, they should see a doctor. A doctor can assess whether or not there is a serious underlying problem.

Anyone anxious or self-conscious about the size of their testicles should talk to a healthcare professional at their next appointment.

It is important to schedule an appointment with a healthcare professional if:

  • pain, shrinking, or swelling occurs in one or both testicles
  • a partner does not become pregnant after a year or more of trying
  • a lump appears in the scrotum
  • unusual breast growth occurs
  • there are symptoms of low testosterone, such as erectile problems or low energy
  • other accompanying symptoms arise, such as lower back pain, shortness of breath, abdominal pain, a cough, confusion, or headaches

Having small testicles does not necessarily mean that a person has a health issue.

However, a sudden change in the size or shape of the testicles could indicate a problem.

Even serious issues, such as testicular cancer, may be easier to treat if a doctor diagnoses them early. Therefore, people should never delay seeking treatment.