Average Adult Testicle Size in the UK
In UK adult men, the mean testicular volume is approximately 19.8 mL (SD 5.4 mL) for both left and right testicles, which corresponds to testicular dimensions that fall well within the normal range. 1
Specific UK Reference Data
A prospective study of 609 Caucasian British men aged 16-90 years established the following reference ranges 1:
- Mean testicular volume: 19.8 mL (standard deviation 5.4 mL) for both testicles 1
- No significant correlation was found between testicular size and age in this adult population 1
- No significant difference existed between right and left testicular volumes 1
Clinical Context: What Constitutes Normal vs. Small Testicles
Testicular volumes less than 12 mL are definitively considered atrophic and associated with significant pathology, including impaired spermatogenesis and increased risk of intratubular germ cell neoplasia 2, 3
- Volumes between 12-15 mL are considered borderline-small and warrant clinical correlation 3
- The 12 mL threshold represents the lower limit of normal, below which further investigation is indicated 3
- Mean testicular size strongly correlates with total sperm count and sperm concentration 3, 4
Measurement Considerations
When testicular volume is measured clinically 3, 5:
- Ultrasound with the Lambert formula (Length × Width × Height × 0.71) provides the most accurate volume estimates 3, 5
- Prader orchidometer readings provide reasonable clinical estimates but may differ slightly from ultrasound measurements 3
- External measurements with calipers systematically overestimate testicular dimensions by including scrotal skin and epididymis 6, 7
Clinical Significance of Testicular Size
Testicular volumes below 12 mL warrant evaluation for 2, 3:
- History of cryptorchidism (undescended testicles), which substantially increases cancer risk 2, 3
- Infertility concerns, as volumes <12 mL are associated with impaired spermatogenesis 3
- Risk of intratubular germ cell neoplasia, particularly in men under 30-40 years with volumes <12 mL (>34% risk in contralateral testis if cancer present) 2, 3
- Hormonal evaluation (FSH, LH, testosterone) to distinguish primary testicular failure from other causes 3, 5
Important Clinical Pitfall
The 4 cm threshold mentioned in cancer guidelines refers to tumor size within the testis, NOT overall testicular dimensions 2—this is a common source of confusion that should be avoided when counseling patients about normal testicular size.