At what testicle volume do most men continue to produce some sperm, specifically those with oligospermia (low sperm count)?

Testicular Volume and Sperm Production Threshold

Most men continue to produce at least some sperm (oligospermia) down to a total testicular volume of approximately 20 mL by ultrasound (equivalent to roughly 30 mL by Prader orchidometry), though individual variation exists and some men maintain sperm production even below these thresholds. 1

Critical Volume Thresholds

Ultrasound Measurements

• Mean sperm density enters the oligozoospermic range when total testicular volume falls below 20 mL by ultrasonography, based on a study of 397 infertile men divided into volume groups 1
• Total sperm count becomes subnormal when total testicular volume drops below 20 mL by ultrasound 1
• Individual testicular volume below 12 mL (or 6 mL per testis) is associated with testicular atrophy and significantly impaired testicular function 2, 1

Prader Orchidometry Measurements

• By Prader orchidometry, mean sperm density becomes oligozoospermic below 35 mL total testicular volume 1
• Total sperm count becomes subnormal below 30 mL by Prader orchidometry 1
• Prader orchidometry consistently overestimates testicular volume by approximately 30-40% compared to ultrasound, so these measurements are not directly comparable 1

Volume-Function Relationship

Linear Correlation Pattern

• All biofunctional sperm parameters (mitochondrial membrane potential, chromatin compactness, DNA fragmentation) show strong negative correlation with decreasing testicular volume (P < 0.0001), demonstrating a near-linear relationship 2
• Testicular volume correlates significantly with sperm concentration (r = 0.25, P < 0.001), sperm output (r = 0.29, P < 0.001), and inhibin B levels (r = 0.42, P < 0.001) 3
• Right testicular volume specifically is the dominant independent predictor of testicular function, with RTV <15 mL being a positive predictor for low testicular function (odds ratio = 2.79) 4

Hormonal Markers

• Testicular volume inversely correlates with serum FSH (r = -0.32, P < 0.001) and LH (r = -0.24, P < 0.001), meaning smaller testes typically present with elevated gonadotropins 3
• Men with non-obstructive azoospermia typically present with low testicular volume, elevated FSH (>7.6 IU/L), and testicular atrophy 5

Important Clinical Caveats

Individual Variation

• Despite severe testicular atrophy, spermatogenesis often persists in small, isolated foci within the testes, meaning some men maintain sperm production even with very small testicular volumes 6
• Up to 50% of men with non-obstructive azoospermia and elevated FSH still have retrievable sperm with microsurgical testicular sperm extraction, despite having atrophied testes 5, 6
• FSH levels and testicular volume alone cannot definitively predict sperm production status—semen analysis remains essential 5

Genetic Factors

• Complete AZFa and AZFb Y-chromosome microdeletions result in almost zero likelihood of sperm retrieval regardless of testicular volume 5, 6
• Karyotype abnormalities including Klinefelter syndrome are established causes of testicular atrophy and impaired spermatogenesis 5

Measurement Considerations

• A single testicular volume measurement should not be used to make definitive conclusions about fertility potential—at least two semen analyses separated by one month are required due to significant intra-individual variability 7
• Ultrasound measurement is more accurate than Prader orchidometry for assessing true testicular volume and predicting function 1

Practical Answer to Your Question

To directly answer your specific volume options:

• 6 mL per testis (12 mL total): This represents the threshold for testicular atrophy, and most men at this volume will have oligospermia or azoospermia, though some may still produce limited sperm 2, 1
• 4 mL per testis (8 mL total): Severe atrophy at this level, with most men having azoospermia, though isolated foci of spermatogenesis may persist 6
• 2 mL per testis (4 mL total): Profound atrophy with very low likelihood of sperm production, though micro-TESE may still retrieve sperm in select cases 6

The most accurate answer is that oligospermia typically begins when total testicular volume falls below 20 mL by ultrasound (approximately 10 mL per testis), with progressive worsening as volume decreases further. 1