What this calculator does
A raised PSA has two broad explanations: a larger prostate producing more of it, or something within the prostate producing more than its size would predict. PSA density separates the two by dividing the level by the volume.
The adjustment can change the reading. A PSA of 4 ng/mL in a 28.3 cc prostate gives a density of 0.141, below the commonly used 0.15 threshold, while a PSA of 8 in the same gland gives 0.283, well above it.
The formula
Prostate volume is calculated as an ellipsoid from three measured dimensions, multiplied by pi over six. PSA is then divided by that volume.
| Term | Meaning |
|---|---|
| PSA density | PSA divided by prostate volume, in ng/mL per cubic centimetre. |
| Ellipsoid formula | Length times width times height times pi/6, the standard prostate volume estimate. |
| 0.15 threshold | A widely cited cut-off above which further evaluation is often pursued. |
The inputs explained
| Field | What to enter |
|---|---|
| PSA level (ng/mL) | Serum PSA in ng/mL. |
| Prostate length (cm) | Prostate length in centimetres, from imaging. |
| Prostate width (cm) | Prostate width in centimetres. |
| Prostate height (cm) | Prostate height in centimetres. |
When to use it
Interpreting a borderline PSA
A large prostate can raise PSA without anything else being wrong, which density accounts for.
Deciding whether to biopsy
Density is one of several inputs into that decision, not the deciding one.
Following PSA over time
Density tracks changes better than the raw level when the gland is also growing.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does PSA level move the density?
The same gland at three PSA levels.
| PSA level | PSA density | Reading |
|---|---|---|
| 2 ng/mL | 0.071 ng/mL/cc | Below 0.15: a lower likelihood, though this does not rule out cancer |
| 4 ng/mL | 0.141 ng/mL/cc | Below 0.15: a lower likelihood, though this does not rule out cancer |
| 8 ng/mL | 0.283 ng/mL/cc | 0.15 or higher: often prompts further evaluation |
Questions
Why does prostate size matter?
Because prostate tissue produces PSA, so a larger gland produces more of it without anything being wrong. Benign enlargement is very common with age, and density is an attempt to correct for it.
How reliable is the volume estimate?
The ellipsoid formula is an approximation, and prostates are not perfect ellipsoids. Measurement varies with imaging method and operator, and that error carries straight into the density.
Is 0.15 a hard threshold?
No. It is a commonly cited figure rather than a diagnostic boundary, and different guidelines and studies use different cut-offs. It shifts the likelihood rather than settling the question.
Can this rule out prostate cancer?
No. A low density lowers the probability but does not exclude anything, and PSA screening decisions involve age, family history, examination findings and imaging. This belongs with a urologist.
For a general weight-for-height baseline, see the BMI calculator. For kidney function from the same bloods, see the creatinine clearance calculator.