Normal Prostate Size
The normal prostate size in adult men is approximately 20 ± 6 grams (or about 20-30 mL in volume), with this weight remaining essentially constant with age unless benign prostatic hyperplasia (BPH) develops. 1
Prostate Size by Age
- Young adults (21-30 years): 20 ± 6 grams 1
- Middle-aged men without BPH: Remains relatively constant at 20 ± 6 grams
- Older men with BPH: Average weight increases to 33 ± 16 grams 1
Measurement Methods and Accuracy
Digital Rectal Examination (DRE)
- DRE tends to underestimate the true prostate size 2
- The underestimation increases with larger prostates:
- 9-12% underestimation for prostates 30-39 mL
- 17-27% underestimation for prostates 40-49 mL 3
Transrectal Ultrasound (TRUS)
- Primary screening tool for evaluating prostatic pathology 4
- More accurate than DRE for determining prostate volume
- Recommended when precise measurements are needed, especially for treatment decisions 2
Clinical Significance of Prostate Size
Treatment Decisions
- Prostates ≤30g: Transurethral incision of the prostate (TUIP) is recommended 2
- Prostates >30g: 5-alpha reductase inhibitors (5-ARIs) like finasteride are more effective 2
- Prostates >60g: May require different surgical approaches; some providers use transurethral approaches (bipolar TURP, HoLEP) while others may consider open, laparoscopic, or robotic-assisted prostatectomy 2
BPH Progression
- Only 8% of men in their 40s have pathological BPH
- 50% of men aged 51-60 have pathological BPH 1
- Only 4% of men over 70 develop prostates larger than 100g 1
Prostate Size Classification by DRE
Based on digital rectal examination findings, prostates can be classified as 5:
- Flat: Median volume 16.4 mL
- Normal: Median volume 18.3 mL
- Slightly enlarged: Median volume 27.0 mL
- Moderately enlarged: Median volume 41.9 mL
- Markedly enlarged: Median volume 86.3 mL
Important Considerations
- Prostate size alone does not determine symptom severity in BPH
- For treatment decisions requiring accurate size assessment (especially for 5-ARI therapy), TRUS or cross-sectional imaging is recommended over DRE 2
- Extremely large prostates are rare but possible - case reports document sizes up to 3987 mL 6
- When evaluating prostate size, it's important to differentiate the prostate proper from surrounding non-prostatic tissue for accurate measurement 7
For clinical practice, understanding normal prostate size is essential for proper evaluation of BPH and selecting appropriate treatments based on prostate volume thresholds.