Prostate Volume Formulas: Ellipsoid vs. Bullet

Accurate prostate volume calculation relies on choosing the right mathematical model. The two most common formulas used in clinical practice are the Ellipsoid formula and the Bullet formula.

1. The Ellipsoid Formula

The Ellipsoid formula is the standard method used in most ultrasound machines and clinical studies. It assumes the prostate is shaped like an ellipsoid (a 3D oval).

• Best for: General screening and standard-shaped prostates.
• Accuracy: Highly accurate for smaller to medium-sized glands (<80cc).
• Origin: Derived from the volume of a sphere (π/6 ≈ 0.52).

2. The Bullet (Cylindrical) Formula

The Bullet formula is often used for larger prostates or those that have a more cylindrical shape, which is common in significant Benign Prostatic Hyperplasia (BPH).

• Best for: Large prostates (>80cc) or glands that appear wider at the base.
• Accuracy: May provide a better estimation for enlarged glands where the ellipsoid formula underestimates volume.

Which One Should You Use?

For the majority of patients, the Ellipsoid Formula (0.52) is the recommended standard. It is the default setting on our calculator and matches the methodology of most urological guidelines.

However, if a patient has a known history of significant BPH or if digital rectal examination suggests a very large gland, a clinician might consider the Bullet formula for a potentially more realistic volume estimate.