Prostate Volume Calculator (Ellipsoid Method)
Use radiology measurements from ultrasound or MRI. Enter AP, transverse, and craniocaudal dimensions, then calculate volume in mL (cc).
Why prostate volume matters in radiology
Prostate volume is a routine metric in genitourinary imaging. It helps clinicians interpret lower urinary tract symptoms, monitor benign prostatic hyperplasia (BPH), and contextualize PSA values. In many reports, volume is expressed in mL (which is numerically equal to cc).
Radiologists commonly estimate volume using the ellipsoid formula based on three orthogonal dimensions. This method is fast, reproducible in daily practice, and aligns with standard reporting workflows in ultrasound and MRI.
Ellipsoid formula used in imaging reports
The most common equation is:
Volume = AP × Transverse × Craniocaudal × 0.52
When dimensions are entered in centimeters, the result is in cubic centimeters (cc), equivalent to mL. If dimensions are measured in millimeters, convert to centimeters first by dividing by 10.
Example
- AP = 3.8 cm
- Transverse = 4.9 cm
- Craniocaudal = 4.4 cm
Volume = 3.8 × 4.9 × 4.4 × 0.52 = 42.6 mL (approximately).
How to measure each dimension correctly
On transrectal ultrasound (TRUS)
- AP diameter: Measured on sagittal or axial view depending on protocol.
- Transverse diameter: Maximal width on axial view.
- Craniocaudal diameter: Maximal length on sagittal view from base to apex.
On prostate MRI
- Use high-resolution T2-weighted images.
- Measure maximal orthogonal dimensions in planes that best represent the gland.
- Document the method if your institution requires PI-RADS-consistent reporting language.
Interpreting prostate volume
Interpretation varies by age, symptoms, and clinical context, but practical volume groupings are often:
- < 30 mL: Smaller to average gland size
- 30–50 mL: Mild to moderate enlargement
- > 50 mL: Significant enlargement commonly seen with BPH
These ranges are not diagnostic alone. They should be integrated with symptom scores, urinalysis, PSA trends, digital rectal exam findings, and treatment goals.
PSA density: a useful companion metric
PSA density is calculated as:
PSA density = PSA (ng/mL) / Prostate volume (mL)
This helps adjust PSA interpretation for gland size. A value above 0.15 ng/mL/cc is often used as a clinical threshold in some contexts, but decisions should follow local guidelines and specialist judgment.
Common pitfalls in prostate volume estimation
- Mixing mm and cm without conversion
- Using non-maximal dimensions
- Inconsistent plane selection across follow-up studies
- Including seminal vesicles or extraprostatic tissue by mistake
- Assuming volume alone confirms diagnosis
Practical reporting tip
For consistency, many radiology reports include both the three measured dimensions and the calculated volume, for example: “Prostate measures 4.9 × 3.8 × 4.4 cm (TR × AP × CC), estimated volume 42.6 mL by ellipsoid method.”
Medical disclaimer
This calculator is for educational and workflow support purposes. It does not replace clinical judgment, institutional protocols, or formal medical advice.