If your doctor mentioned your PSA is elevated, one of the first questions worth asking is: "elevated compared to what?" A PSA of 6.0 ng/mL means something very different in a man with a 20 cc prostate than it does in a man with a 60 cc prostate. That's where prostate volume and PSA density come in.
This calculator takes your prostate dimensions from an ultrasound or MRI report and converts them into a volume estimate using the standard ellipsoid formula. Pair that with your PSA blood test result, and you get your PSA density — a number that helps put your PSA into proper context. Whether you're a urologist checking numbers between patients or someone sitting at home trying to make sense of your imaging report before your next appointment, this tool gives you a clearer starting point for that conversation.
What Is Prostate Volume and Why Does It Matter?
Your prostate is a small gland — roughly the size of a walnut in younger men — that sits just below the bladder. Its volume is measured in cubic centimeters (cc), and in a man under 40, a typical prostate measures about 20-25 cc.
Here's why that number matters more than most people realize.
The prostate grows with age. By the time a man reaches his 60s or 70s, his prostate may be 40, 50, or even 80+ cc. This growth is usually benign prostatic hyperplasia (BPH) — not cancer — but a bigger prostate naturally produces more PSA. So when a blood test comes back with a PSA of 7.0 ng/mL, the critical follow-up question is whether that's a lot of PSA for the size of the gland producing it.
Prostate volume also drives treatment decisions. A 35 cc prostate with urinary symptoms might respond well to medication alone, while a 90 cc prostate causing the same symptoms may need a completely different surgical approach. And when it comes to cancer screening, knowing the volume helps your urologist decide whether a biopsy is warranted or whether your PSA is likely explained by a large but benign gland.
Without prostate volume, a PSA result can easily create unnecessary anxiety — or worse, false reassurance.
Understanding PSA Density
PSA density answers a simple question: is your PSA level proportionate to the size of your prostate?
The formula is straightforward:
PSA Density = PSA (ng/mL) / Prostate Volume (cc)
A bigger prostate produces more PSA. That's normal biology. PSA density adjusts for this by dividing your PSA by your gland volume, giving you a per-unit-of-tissue value that's more clinically meaningful than PSA alone.
To see why this matters, consider two men who both have a PSA of 5.0 ng/mL:
- Man A has a 50 cc prostate. His PSA density is 5.0 / 50 = 0.10 ng/mL/cc. His elevated PSA is most likely explained by the size of his gland.
- Man B has a 25 cc prostate. His PSA density is 5.0 / 25 = 0.20 ng/mL/cc. That's a higher concentration of PSA per cc of tissue — something his urologist will want to investigate further.
Same PSA. Very different clinical picture.
The most commonly used threshold is 0.15 ng/mL/cc. Below that, an elevated PSA is more likely related to gland size. Above it, further evaluation — potentially including an MRI or biopsy — is often recommended. But this threshold isn't a hard line. Your doctor weighs it alongside your age, family history, how fast your PSA has been rising, and what your imaging looks like.
How Prostate Volume Is Measured
Prostate volume is estimated from imaging using the ellipsoid formula:
Volume = Length x Width x Height x pi/6
The pi/6 factor (approximately 0.52) models the prostate as an ellipsoid — a shape that closely approximates the real anatomy in most men. This is the same formula used at major academic centers and referenced in AUA and EAU guidelines.
Imaging Methods
Method | How It Works | When It's Used |
|---|---|---|
Transrectal Ultrasound (TRUS) | Ultrasound probe measures three dimensions directly | Most common clinical method; often done during biopsy planning |
MRI | Multiparametric imaging provides highly detailed measurements | Gold standard for accuracy; part of PI-RADS assessment |
CT Scan | Cross-sectional imaging estimates dimensions | Less accurate for prostate specifically; used when MRI isn't available |
Which Measurements Do You Need?
Your radiology report will list three dimensions, usually in centimeters:
- Length (anteroposterior/AP): The front-to-back measurement, taken from a sagittal image
- Width (transverse/TR): The side-to-side measurement, taken from an axial image
- Height (craniocaudal/CC): The top-to-bottom measurement, from a sagittal or coronal image
If your report lists something like "prostate measures 4.2 x 3.8 x 3.5 cm," those three numbers are exactly what you need. If you're not sure which dimension is which, your radiologist or urologist can clarify.
How to Use This Calculator
- Enter your prostate length — the anteroposterior (AP) measurement from your imaging report. Use the dropdown to select whether your report lists it in centimeters or millimeters.
- Enter your prostate width — the transverse measurement. Match the unit to your report.
- Enter your prostate height — the craniocaudal (CC) measurement, again with the correct unit selected.
- Check your calculated volume. It appears instantly. You can toggle the output between cubic centimeters (cc) and cubic millimeters using the volume unit dropdown. For PSA density, you'll want the result in cc.
- Enter your PSA level in ng/mL. This is on your blood test results, typically labeled "PSA, Total" or "Prostate-Specific Antigen."
- Review your PSA density. The calculator divides your PSA by your prostate volume and displays the result.
Worked Example
Say your MRI report shows prostate dimensions of 4.2 x 3.8 x 3.5 cm, and your most recent PSA is 6.2 ng/mL.
- Enter 4.2 as length, 3.8 as width, 3.5 as height (all in cm)
- The calculator computes: 4.2 x 3.8 x 3.5 x 0.5236 = 29.3 cc
- Enter PSA of 6.2
- PSA density: 6.2 / 29.3 = 0.21 ng/mL/cc
In this case, the PSA density of 0.21 is above the 0.15 threshold, which your urologist would factor into decisions about next steps — alongside your age, imaging findings, and other clinical details.
Understanding Your Results
What's a Normal Prostate Volume?
Prostate volume depends heavily on age. What's considered normal for a 45-year-old would be unusual in a 75-year-old, and vice versa.
Volume | Classification | Context |
|---|---|---|
Under 25 cc | Normal | Typical for men under 40-50 |
25-30 cc | Upper normal | Often normal in men over 50 |
30-50 cc | Mildly enlarged | Common with BPH in men over 50; may or may not cause symptoms |
50-80 cc | Moderately enlarged | More likely to affect urinary flow |
Over 80 cc | Significantly enlarged | Often requires treatment consideration |
An important nuance: symptoms don't always track with size. Some men with a 60 cc prostate urinate just fine, while others with a 35 cc gland have significant difficulty. The pattern of enlargement — particularly whether it pushes into the urethra — matters as much as the volume itself.
PSA Density: What the Numbers Mean
PSA Density | What It Suggests |
|---|---|
Below 0.10 ng/mL/cc | Reassuring — PSA elevation is likely proportionate to prostate size |
0.10-0.15 ng/mL/cc | Gray zone — your doctor will weigh other factors like age, family history, and PSA trend |
Above 0.15 ng/mL/cc | Higher concern — further evaluation (MRI, biopsy) is often discussed |
Above 0.20 ng/mL/cc | Elevated — biopsy is more commonly recommended, depending on the full clinical picture |
The good news is that many men with PSA density above 0.15 turn out to have benign findings on biopsy. A higher density raises the index of suspicion, but it doesn't mean cancer is present. It means the question is worth investigating.
Age-Adjusted Context
Because both prostate volume and PSA rise with age, here's a rough sense of what's typical:
Age Range | Average Prostate Volume | Typical PSA Range |
|---|---|---|
40-49 | 20-25 cc | 0-2.5 ng/mL |
50-59 | 25-35 cc | 0-3.5 ng/mL |
60-69 | 30-45 cc | 0-4.5 ng/mL |
70-79 | 35-55 cc | 0-6.5 ng/mL |
These are population averages. Your individual numbers depend on genetics, lifestyle, and whether you have BPH or other conditions. But this gives you a frame of reference for interpreting your results.
Factors That Can Affect Your Results
Both sides of the PSA density equation — prostate volume and PSA level — can be influenced by factors that have nothing to do with cancer. It's worth knowing about these before drawing conclusions from your numbers.
On the volume side, different imaging methods can produce slightly different measurements. MRI tends to be more reproducible than ultrasound, and the operator's technique — where exactly they place the measurement calipers — introduces some variability. The ellipsoid formula also assumes a fairly symmetric gland shape, which works well for most prostates but can over- or underestimate volume in unusually shaped glands.
On the PSA side, several things can temporarily raise your levels. A urinary tract infection or prostatitis can push PSA up significantly. Ejaculation within 24-48 hours of a blood draw may elevate it modestly. Even vigorous cycling has been reported to affect PSA in some men. And if you take finasteride or dutasteride (common BPH medications), your measured PSA is artificially reduced by about 50% — so you'd need to double your result to get a truer picture.
If your PSA was drawn during an infection, shortly after a procedure, or while on medications that affect PSA, bring that up with your doctor. The timing matters, and a repeat test under better conditions may be warranted before making any decisions.
Preparing for Your Doctor's Appointment
If you're using this calculator to prepare for a conversation with your urologist, here are a few things that can make that appointment more productive:
- Bring your actual imaging report. Your doctor will want to see the specific measurements and any additional findings the radiologist noted, not just the volume number.
- Know your PSA history. A single PSA value is less informative than the trend over time. If you can, bring your last 2-3 PSA results with dates.
- Write down your questions. It's easy to forget what you wanted to ask once you're in the room. Even simple questions — "Is my PSA density concerning?" or "Should we do an MRI?" — are worth putting on paper.
- Note any medications you're on. Especially finasteride, dutasteride, or testosterone therapy, since these directly affect PSA levels.
Remember that your urologist sees these numbers every day. What feels alarming on a lab report often looks very different when placed in the full clinical context.
Technical Notes
Formulas used:
- Prostate Volume (cc) = Length (cm) x Width (cm) x Height (cm) x pi/6
- PSA Density (ng/mL/cc) = PSA (ng/mL) / Prostate Volume (cc)
- pi/6 = approximately 0.5236, commonly rounded to 0.52 in clinical practice
Unit conversions:
- 1 cc = 1 mL = 1,000 mm3
- Inputs in millimeters are converted to centimeters before volume calculation
Clinical references:
- The ellipsoid formula is endorsed by the American Urological Association (AUA) and the European Association of Urology (EAU) for estimating prostate volume from imaging.
- The 0.15 ng/mL/cc PSA density threshold is referenced in active surveillance guidelines and multiple biopsy decision frameworks.
Disclaimer: This calculator is for educational and informational purposes only. It does not provide medical advice, diagnosis, or treatment recommendations. Always consult a qualified healthcare professional about your specific situation. Clinical decisions should never be based solely on calculator results.