What is the normal size and shape of an adult male's testis?

Normal Adult Testicular Size and Shape

Standard Dimensions

The normal adult testis is ovoid in shape and measures 3.5 to 5 cm in length, corresponding to a volume typically greater than 12-14 mL, with volumes below 12 mL considered pathologically small and warranting further investigation. 1

Volume Standards by Population

• Japanese populations: Normal adult testicular volume is greater than 14 mL 2
• American populations: Normal adult testicular volume is greater than 17 mL 2
• Universal threshold: Volumes below 12 mL are universally considered small or atrophic regardless of population 1

Width Measurements

• Normal adult testicular width ranges from 2 to 3 cm 1
• The testis maintains an ovoid (ellipsoid) shape throughout adulthood 1

Clinical Significance of Size Thresholds

Testicular volumes below 12 mL are definitively pathological and associated with significant clinical concerns 1:

• Impaired spermatogenesis: Strong correlation exists between testicular volume and total sperm count/concentration 3
• Cancer risk: Men under 30-40 years with volumes <12 mL have a >34% risk of intratubular germ cell neoplasia (GCNIS) in the contralateral testis if testicular cancer develops 4, 1
• Fertility implications: Volumes below 12 mL strongly predict reduced fertility potential 3

Borderline-Small Testes

• Volumes between 12-15 mL are considered borderline-small and warrant clinical correlation 1
• These patients require semen analysis and hormonal evaluation to assess functional status 1

Measurement Methods

Clinical Assessment

The Prader orchidometer is the preferred tool for rapid clinical assessment, though it tends to overestimate volume compared to ultrasound 1, 5:

• Simple, cost-effective, and readily available for routine clinical use 5
• Provides good surrogate for volume in most clinical scenarios 6
• Normal adult range: >14-17 mL depending on population 2

Ultrasound Measurement

Ultrasound is the gold standard for accurate volume determination but should be reserved for specific indications 1, 7:

• Use high-frequency probes (>10 MHz) to maximize resolution 6
• Calculate volume using the Lambert formula: Length × Width × Height × 0.71 1
• Avoid the traditional ellipsoid formula (0.52 coefficient) as it systematically underestimates volume by 20-30% 1

Indications for Ultrasound

Ultrasound is recommended when 6, 7:

• Large hydrocele obscures physical examination
• Inguinal testis location
• Epididymal enlargement or fibrosis
• Thickened scrotal skin
• Size discrepancy between testes >2 mL or 20%

Common Pitfalls to Avoid

Measurement Errors

• Do not use the 0.52 ellipsoid formula for clinical decision-making, as it leads to inappropriate classification of testicular atrophy 1
• Ensure proper caliper placement during ultrasound to avoid technical errors that can falsely suggest severe atrophy 1
• Use the same sonographer for serial measurements when possible to minimize inter-scan variability 1

Clinical Interpretation

• Avoid hunting for subclinical varicoceles with ultrasound—only palpable varicoceles benefit from treatment 6, 1
• Do not rely on testicular volume alone to predict fertility; always obtain semen analysis when fertility is a concern 1
• Clinical methods (ruler, orchidometer) overestimate ultrasound volumes by 70-80% in adults due to inclusion of scrotal skin and epididymis 8

Risk Factors for Small Testes

History of cryptorchidism is the single most important risk factor for testicular atrophy and should always be elicited 4, 1:

• Significantly increases risk of both atrophy and testicular cancer 4, 1
• Even the contralateral descended testis may have structural abnormalities including smaller volume 6

High-Risk Scenarios Requiring Further Workup

When testicular volume is <12 mL, additional evaluation is mandatory if 1:

• Age under 30-40 years (≥34% risk of GCNIS)
• History of cryptorchidism
• Presence of testicular cancer in one testis
• Infertility concerns with bilateral small testes

Recommended Actions for Small Testes

• Obtain detailed history focusing on cryptorchidism, infertility, and family history of testicular cancer 1
• Perform semen analysis to assess sperm concentration, motility, and morphology 1
• Measure serum FSH, LH, and testosterone to distinguish primary testicular failure from secondary causes 1
• Consider karyotype testing if severe oligospermia (<5 million/mL) or azoospermia is present 1
• Teach testicular self-examination given increased cancer risk 6, 1
• Refer for testicular biopsy if high-risk features are present 1