Normal Adult Testicular Size
In healthy adult males with no medical history, normal testicular volume ranges from 15-25 ml (approximately 4-5 cm in length), with volumes below 12 ml considered atrophic and associated with impaired spermatogenesis. 1
Standard Measurement Parameters
Volume-Based Assessment
- The lower limit of normal testicular volume is approximately 12 ml, below which testes are considered small or atrophic and warrant further investigation 2, 1
- Normal adult testicular volume typically ranges from 15-25 ml, which corresponds to the size comparisons mentioned (large olive to small plum) 1
- The American Urological Association suggests that a testicular volume of 12 ml represents the lower limit of normal, with 4 cm testicular length corresponding to approximately 15-18 ml volume 1
Length-Based Measurements
- Normal adult testicular length in Japan is greater than 14 ml (measured by orchidometer), while in the United States it is greater than 17 ml 3
- A 4 cm testicular length corresponds to a volume of approximately 15-18 ml, which falls within the normal range 1
Clinical Measurement Methods
Orchidometer Assessment
- The Prader orchidometer is the gold standard for clinical testicular volume measurement, providing a good surrogate for ultrasound volume while being easier to perform and more cost-effective 1
- The orchidometer consists of a graded series of elliptical models with volumes indicated, allowing rapid bedside assessment 3
Ultrasound Calculation
- When using ultrasound, the Lambert formula (Length × Width × Height × 0.71) provides the most accurate volume estimates compared to the traditional ellipsoid formula 1
- The traditional ellipsoid formula (0.52 coefficient) systematically underestimates testicular volume by 20-30% and should not be used for clinical decision-making 1
Clinical Significance of Size
Correlation with Function
- Mean testicular size strongly correlates with total sperm count and sperm concentration, with the strongest correlation being with serum FSH levels 1, 4
- Testicular volumes less than 12 ml are associated with impaired spermatogenesis, higher risk of intratubular germ cell neoplasia, and potential infertility 1
Size Discrepancy
- A size discrepancy between testes greater than 2 ml or 20% warrants ultrasound evaluation to exclude pathology, regardless of absolute volume 1
Common Pitfalls
Measurement Errors
- High-frequency probes (>10 MHz) should be used for ultrasound measurement to maximize resolution and accurate caliper placement 1
- Measurements should include three perpendicular dimensions (length, width, height) on axial slices, with the same sonographer performing serial measurements when possible 1
Clinical Context Matters
- Testicular volume alone cannot definitively predict fertility status—even "normal-sized" testes should prompt semen analysis in the context of infertility 1
- In men under 30 years with testicular volume <12 ml and history of cryptorchidism, there is a >34% risk of intratubular germ cell neoplasia in the contralateral testis if testicular cancer is present 1