PSA Density Calculator (PSA ÷ prostate volume, 0.15 threshold)

Understanding the PSA density calculator — concept and principle

PSA density divides the blood PSA level by the prostate volume. It helps tell whether a raised PSA is more likely due to a large benign prostate or to cancer, and is used with MRI to decide who needs a biopsy.

PSA per mL of prostate: with the default inputs the result is 0.133 (below 0.15).

How it is calculated

PSA density (ng/mL per mL) = PSA (ng/mL) ÷ prostate volume (mL)

PSA at which density reaches 0.15 = 0.15 × volume

Prostate volume usually comes from transrectal ultrasound or MRI, using length × width × height × π ÷ 6.
The traditional cut-off is 0.15.

The principle

Both normal and cancerous prostate tissue make PSA, but cancer releases more PSA per gram of tissue. A large benign gland can raise PSA simply because there is more tissue. Dividing by volume corrects for size, so a high density points more towards cancer than a high PSA in a large gland does.

Worked example

Default inputs: PSA 6 ng/mL, prostate volume 45 mL.

PSA density = 6 ÷ 45 = 0.133.
0.133 is Below 0.15.
PSA at which density would reach 0.15 = 0.15 × 45 = 6.75 ng/mL.

Each point is the calculator re-run with only “Prostate volume (mL or cm³)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Prostate volume (mL or cm³)	PSA density (ng/mL per mL)
11.2	0.533
22.5	0.267
33.8	0.178
45	0.133
56.2	0.107
67.5	0.089
90	0.067

How to read the result

Where does your result fall?

A density of 0.15 or more is associated with a higher chance of clinically significant prostate cancer. Some MRI-based pathways use thresholds between 0.10 and 0.20 depending on the MRI score. A low density with a reassuring MRI may allow surveillance instead of biopsy, but decisions depend on the full picture.

Common mistakes

Measuring PSA soon after ejaculation, cycling, infection or a catheter, which raises it temporarily.
Forgetting that finasteride and dutasteride roughly halve PSA.
Using a rough volume estimate from a transabdominal scan.

Keep in mind: This is not a diagnosis. Decisions about prostate biopsy or treatment should be made with a urologist.

Frequently asked questions

What is a normal PSA density?

Below 0.15 is the traditional reassuring range, though no level fully excludes cancer.

Why does prostate size matter?

Larger glands make more PSA even without cancer.

Is PSA density used with MRI?

Yes. It helps decide on biopsy, especially when the MRI is equivocal.

Sources: Benson MC, Whang IS, Pantuck A, et al., "Prostate specific antigen density: a means of distinguishing benign prostatic hypertrophy and prostate cancer", J Urol 1992;147(3 Pt 2):815–816

Checked 9 Nov 2026. Standard definition PSAD = PSA ÷ prostate volume with the conventional 0.15 ng/mL/mL threshold (Benson MC et al., J Urol 1992); ellipsoid prostate volume formula (standard).

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