Is your testicle size normal? Here is what the data says.

Testicle size is correlated with sperm production, as the seminiferous tubules (where sperm are made) comprise approximately 80% of testicular volume. Studies have found a positive correlation between testicle volume and sperm count. However, men with smaller testicles can have normal sperm counts, and a semen analysis is a far more direct measure of fertility.

A painless lump or swelling in one testicle is the most common sign. Other signs include a feeling of heaviness in the scrotum, a dull ache in the lower abdomen or groin, sudden fluid build-up, or a change in the way a testicle feels. Pain is present in only about 10-20% of cases at diagnosis. Testicular cancer is the most common cancer in men aged 15-44 but has a cure rate exceeding 98% when caught early. If you notice any changes, see a doctor within 1-2 weeks. (Sources: Cancer Research UK; NHS; Testicular Cancer Society.)

The Testicular Cancer Society recommends a monthly self-exam, ideally during or after a warm shower when the scrotal skin is relaxed. Hold each testicle between your thumb and fingers and roll it gently, feeling for any hard lumps, smooth bumps, or changes in size or texture. The epididymis (a soft, tube-like structure at the back of the testicle) is normal and should not be mistaken for a lump. If you find anything unusual, book a GP or urologist appointment. Most lumps are not cancer (cysts and varicoceles are more common), but all new lumps should be checked. (Sources: Testicular Cancer Society; NHS.)

Testicle size increases during puberty, reaching adult dimensions by age 16-18. Peak size is maintained through the 20s-40s. Some studies suggest a gradual decline in volume after age 50, associated with decreasing testosterone production. The decline is modest in most men. Significant shrinkage (testicular atrophy) can be caused by varicocele, hormonal disorders, alcohol misuse, or anabolic steroid use, and should be medically evaluated. (Sources: EAU; Prader orchidometer reference data.)

There is a correlation, but it is not as strong as many people assume. Leydig cells, which produce testosterone, make up only about 10-20% of testicular volume. Men with clinically small testicles may have lower testosterone, particularly in conditions such as Klinefelter syndrome or hypogonadism. However, testosterone levels are influenced by many factors beyond testicle size, including body fat, age, sleep, stress, and genetics. A blood test is the only way to accurately assess testosterone levels. (Sources: EAU Guidelines on Male Hypogonadism.)

Testicular atrophy can be caused by: anabolic steroid use (one of the most common causes in younger men, as exogenous testosterone suppresses the body's own production), varicocele (enlarged veins in the scrotum causing progressive atrophy), hormonal imbalances, excessive alcohol consumption, certain medications, infections such as mumps orchitis, testicular torsion, and ageing. If you notice a significant change in testicle size, consult a urologist. In many cases, the underlying cause is treatable. (Sources: EAU; NHS.)

You can estimate testicle size at home using a ruler or measuring tape. Measure the length (top to bottom) and width (side to side) of each testicle. The approximate volume can be calculated using the ellipsoid formula: Volume = 0.71 x length x width x depth (all in cm), giving a result in mL. For an accurate measurement, urologists use a Prader orchidometer (a string of calibrated beads) or ultrasound. Home measurements are useful for self-monitoring but are less precise than clinical measurement. (Sources: Sakamoto et al., 2007.)