What percentage size difference between testicles (testes) is considered normal without causing concerns?

Normal Testicular Size Difference

A testicular size difference of up to 20% between the left and right testicle is considered normal and does not cause concern. 1

Understanding Normal Testicular Asymmetry

• Testicular asymmetry is common in healthy males, with studies showing that approximately 58.8% of healthy adolescent boys have a smaller left testicle compared to the right 2
• The European Association of Urology guidelines specifically note that a size difference of up to 20% (or 2 ml) between testicles is considered within normal physiological variation 1
• Mean testicular volumes in healthy adult males are approximately 14.1 ml for the right testicle and 13.0 ml for the left testicle, demonstrating that some natural asymmetry is expected 3

Clinical Significance of Testicular Size Differences

• A testicular size difference becomes clinically significant when:

  • The difference exceeds 20% of the larger testicle volume 1
  • The absolute volume difference is greater than 2 ml 2
  • One testicle is smaller than 12 ml (considered atrophic) 4

• When evaluating testicular size differences, ultrasound is the established first-line imaging modality that can accurately measure testicular dimensions 1

Concerning Findings That Warrant Further Investigation

• Size differences exceeding 20% may indicate underlying pathology and should prompt further evaluation 1
• Testicular volumes less than 12 ml are generally considered small or atrophic and may warrant additional investigation 4
• In adolescents with varicocele, a persistent size difference of >2 ml or >20% between testicles (confirmed on two visits 6 months apart) is an indication for surgical intervention 1

Measurement Methods

• Testicular volume can be measured using:
  • Prader orchidometer (clinical practice standard) 4
  • Ultrasound measurement using the Lambert formula (length × width × height × 0.71) for more precise evaluation 5, 6
  • The Testicular Atrophy Index (TAI) can be calculated using the formula [(TV right - TV left)/largest TV] × 100 2

Clinical Implications of Testicular Size

• Mean testicular size strongly correlates with sperm parameters including total sperm count and sperm concentration 7, 6
• Testicular volumes below 10 ml, length below 3.5 cm, depth below 1.5 cm, or width below 2.25 cm are associated with subnormal sperm counts 6
• Smaller testicular size (<12 ml) may be associated with higher risk of intratubular germ cell neoplasia and impaired spermatogenesis 4

When to Seek Medical Evaluation

• Medical evaluation is recommended when:
  • Testicular size difference exceeds 20% or 2 ml 1, 2
  • Either testicle is smaller than 12 ml 4
  • There is acute onset of scrotal pain 1
  • There are palpable abnormalities or changes in testicular consistency 1

Remember that while some asymmetry is normal, any concerning changes in testicular size, shape, or consistency should be evaluated by a healthcare provider to rule out underlying pathology.