Introduction
The Prostate Volume Calculator tells you how big a prostate gland is. You enter three measurements from an ultrasound or MRI scan — length, width, and height — and the tool does the math for you.
It gives you two answers. The ellipsoid volume uses the classic formula (π/6 × L × W × H). The bullet volume uses a slightly different formula (5π/24 × L × W × H) that matches the real shape of the gland more closely. For glands under 55 mL, the bullet result is often the better guess, so it is shown as the preferred one.
The calculator also sorts the result into a size group: normal (under 30 mL), mildly enlarged (30–50 mL), moderately enlarged (50–80 mL), or significantly enlarged (80 mL and up). An enlarged prostate is linked to BPH (benign prostatic hyperplasia), which can make it hard to pee.
If you add a PSA blood test number, the tool also works out PSA density. This is PSA divided by prostate volume. Doctors often look at 0.15 ng/mL² as a key mark, since higher numbers can mean more risk.
You can enter sizes in centimeters, millimeters, or inches, and show the volume in mL, cm³, liters, cubic inches, or fluid ounces. If you need to switch between measurement systems first, our Cm to Inches Calculator and Mm to Inches Calculator can help. A scaled picture, a chart, and a step-by-step solution show exactly how the answer was found. This tool is for learning and support only — always talk to your doctor about your results.
How to use our Prostate Volume Calculator
Enter the three prostate measurements from your ultrasound or MRI report, and add a PSA value if you have one. The calculator gives you the ellipsoid volume, the bullet volume, a prostate size rating, and your PSA density.
Prostate Length (L): Type the longest measurement of the gland from top to bottom. Pick cm, mm, or inches from the drop-down next to the box.
Prostate Width (W): Type the side-to-side (transverse) measurement. Choose the unit that matches your report.
Prostate Height (H): Type the front-to-back (anteroposterior) measurement. Again, set the unit to cm, mm, or inches.
PSA Value (ng/mL): This one is optional. Add your blood PSA number to get PSA density, or leave the box empty to skip it.
Display volume in: Choose how you want the answer shown — mL, cm³, litres, cubic inches, or fluid ounces. Note that 1 mL is the same as 1 cm³. For other unit swaps, see the Volume Conversion Calculator.
Calculate: Click this button to see your prostate volume, size class, chart, and step-by-step math. Click Clear / Reset to start over with sample numbers.
What Is Prostate Volume?
The prostate is a small gland in men. It sits under the bladder and wraps around the urethra, the tube that carries urine out of the body. Prostate volume is the size of that gland, measured in milliliters (mL). One mL is the same as one cubic centimeter (cm³).
A healthy adult prostate is about 20 to 30 mL, close to the size of a walnut. The gland often grows with age. When it gets too big, it can press on the urethra and make it hard to pee. If bladder emptying is a concern, the PVR Calculator and Urine Output Calculator cover related urology measures.
How Prostate Volume Is Measured
A doctor uses an imaging scan to measure three lengths of the gland:
- Length (L) — top to bottom, seen from the side view
- Width (W) — side to side, the widest part
- Height (H) — front to back, also called anteroposterior
These three numbers usually come from a transrectal ultrasound (TRUS), an MRI, or a CT scan. The scan gives the sizes in centimeters or millimeters. Then a formula turns those three lengths into a volume.
The Two Formulas
Ellipsoid formula: Volume = (π ÷ 6) × L × W × H. This treats the prostate like a smooth egg shape. It is the oldest and most common method, and it is the same idea behind a general Sphere Volume Calculator stretched along three axes.
Bullet formula: Volume = (5π ÷ 24) × L × W × H. This treats the gland like a bullet, round on one end and flatter on the other. The bullet answer is about 25% larger than the ellipsoid answer. You can check that gap yourself with the Percent Difference Calculator.
Studies show the bullet formula matches the true weight of the gland more closely, especially for glands under about 55 mL. That is why it is marked as the preferred result here. For volumes of other shapes, the general Volume Calculator handles cubes, cones, cylinders, and more.
Prostate Size Classification
| Volume | Meaning |
|---|---|
| Under 30 mL | Normal size |
| 30 – 49 mL | Mildly enlarged |
| 50 – 79 mL | Moderately enlarged |
| 80 mL and up | Significantly enlarged |
An enlarged prostate is called benign prostatic hyperplasia, or BPH. "Benign" means it is not cancer. Size helps doctors pick a treatment. Bigger glands often respond better to certain drugs, and very large glands may need a different type of surgery.
What Is PSA Density?
PSA stands for prostate-specific antigen. It is a protein made by the prostate that shows up in a blood test. A big prostate makes more PSA even when nothing is wrong. So a high PSA alone can be confusing.
PSA density fixes that problem. It divides the PSA level by the prostate volume:
PSA Density = PSA (ng/mL) ÷ Prostate Volume (mL)
The answer is in ng/mL². A value of 0.15 ng/mL² or higher is the common cutoff that raises concern. It suggests the PSA may be high because of cancer, not just because the gland is large. A value below 0.15 more often points to simple enlargement. Doctors use PSA density, along with age, exam findings, and MRI results, to decide if a biopsy is needed. Other imaging-based risk scores work the same way — see the TIRADS Calculator for thyroid nodules or the Adrenal Washout Calculator for adrenal lesions.
Why This Number Matters
Prostate volume is used to track growth over time, plan surgery, calculate radiation doses, and judge how well a treatment is working. It also helps explain urinary symptoms like a weak stream, waking up at night to pee, or trouble starting. Kidney function often gets checked at the same visit, which is where the GFR Calculator, Creatinine Clearance Calculator, and BUN Creatinine Ratio Calculator come in.
Keep in mind that volume alone does not tell the whole story. Some men with large glands have no symptoms, and some with small glands have bad ones. Body size can matter too when dosing or comparing scans, so the BSA Calculator and BMI Calculator are useful companions. Always review your results with your doctor.