Normal Prostate Size
A normal prostate volume is approximately 20-30 mL in younger adult men, with volumes up to 30-40 mL considered borderline enlarged, and anything above 40 mL generally considered enlarged. 1
Age-Specific Normal Ranges
The prostate undergoes continuous growth throughout adult life, making age-specific reference values essential:
Ages 21-30 years: Normal prostate weight is approximately 20 grams (±6 gm), which remains essentially constant unless benign prostatic hyperplasia (BPH) develops 2
Clinical Context from BPH Studies
Multiple large clinical trials provide real-world reference data for symptomatic populations:
American men with lower urinary tract symptoms (LUTS): Mean baseline prostate volume was 36.3 mL (SD 20.1) 5, 1
Multinational cohorts with moderate-to-severe LUTS: Mean volume 54.5 cm³ 5, 1
Clinical Significance Thresholds
Prostate volume directly impacts treatment selection and disease progression risk:
<30 mL: Considered for transurethral incision of the prostate; 5-alpha reductase inhibitors (5-ARIs) show minimal benefit at this size 5, 6
30-80 mL: Standard range for transurethral resection of the prostate (TURP); 5-ARIs demonstrate optimal efficacy when combined with PSA >1.5 ng/mL 5, 6
>80 mL: Open prostatectomy or enucleation techniques recommended; conservative management possible but clinical progression occurs in approximately 33% of cases 5, 7
Growth Patterns and Prevalence
Understanding natural history helps contextualize individual measurements:
Pathological BPH prevalence: Only 8% at age 40-49 years, but reaches 50% by ages 51-60 years 2
Early growth phase (ages 31-50): Doubling time of 4.5 years 2
Mid growth phase (ages 51-70): Doubling time slows to 10 years 2
Late phase (>70 years): Doubling time exceeds 100 years; only 4% of prostates exceed 100 grams 2
Important Clinical Caveats
Prostate volume alone does not predict symptom severity. The correlation between prostate size and International Prostate Symptom Score (IPSS) is weak (r = 0.14-0.18), meaning men with smaller prostates can have severe symptoms and vice versa 4. However, larger prostates (>40 mL) predict better response to finasteride, with greater magnitude of symptom improvement and urinary flow rate enhancement 8.
Ethnic variations exist but are poorly characterized. Most reference data comes from predominantly Caucasian populations (82-95% white), limiting generalizability to other ethnic groups 5, 1.
Measurement method matters. Transrectal ultrasound (TRUS) is the gold standard, though transabdominal ultrasound and MRI are also used. Volume is calculated using the ellipsoid formula: height × width × length × 0.52 3, 9.