PSA (Total) Unit Converter
PSA (Total) Unit Converter
Convert total PSA between ng/mL, µg/L and pmol/L, with age-specific limits and an honest account of the 4.0 ng/mL convention — a referral threshold, not a diagnosis.
PSA (Total) converter
Mass ⇄ molarTotal PSA 3.2 ng/mL, read against the conventional 4.0 ng/mL threshold
Formula and conversion factors
pmol/L = ng/mL × 35.1741
PSA density = total PSA ÷ prostate volume (mL)
- ng/mL = µg/L
- a nanogram per millilitre and a microgram per litre are the same concentration, so nothing is calculated between them
- 35.1741
- derived from a molecular mass of 28,430 Da — the same protein, and therefore the same factor, as free PSA. Molar reporting of PSA is essentially unknown and no threshold is written in pmol/L
- 5-alpha reductase inhibitors
- finasteride and dutasteride roughly halve PSA within six to twelve months, so a man on either needs his result doubled before it is compared with any threshold
- assay dependence
- PSA assays are calibrated against WHO or Hybritech standards, which differ by roughly 20 per cent; follow a man on one laboratory and one assay
Worked example
Total PSA 3.2 ng/mL, read against the conventional 4.0 ng/mL threshold
3.2 ng/mL = 3.20 µg/L — the two units are identical
3.2 × 35.1741 = 112.6 pmol/L
Below the conventional threshold of 4.0 ng/mL, and below the 3.5 ng/mL limit often quoted for men aged 50–59
If this man took finasteride, the untreated equivalent would be about 6.4 ng/mL — above both
Thresholds across the units
| ng/mL | pmol/L | |
|---|---|---|
| Age 40–49, age-specific limit | 2.5 | 87.9 |
| Age 50–59, age-specific limit | 3.5 | 123.1 |
| Age 60–69, age-specific limit | 4.5 | 158.3 |
| Age 70–79, age-specific limit | 6.5 | 228.6 |
| Conventional referral threshold, any age | 4.0 | 140.7 |
| The grey zone where free:total ratio and PSA density help | 4.0 – 10.0 | 140.7 – 351.7 |
What moves PSA without any cancer
| Cause | Direction and size | What to do |
|---|---|---|
| Benign prostatic enlargement | Up, roughly in proportion to gland volume | PSA density adjusts for it |
| Prostatitis or urinary infection | Up, sometimes several-fold | Treat, then repeat after four to six weeks |
| Acute urinary retention, catheterisation, cystoscopy, biopsy | Up, markedly and for weeks | Delay the test rather than interpret it |
| Ejaculation within 48 hours | Up, modestly | Repeat after 48 hours of abstinence |
| Finasteride or dutasteride | Down, roughly halved after six to twelve months | Double the measured value before comparing it with a threshold |
| Change of assay or laboratory | Either way, by up to about 20 per cent | Follow a serial trend on one assay only |
What the 4.0 ng/mL number actually is
Total PSA is reported in ng/mL, and in the numerically identical µg/L, so there is nothing to calculate between those two. The pmol/L column uses a factor of 35.1741, derived from a molecular mass of 28,430 daltons — the same protein and the same factor as free PSA, since free and complexed PSA differ in what they are bound to rather than in what they are. Molar reporting of PSA is essentially unheard of, and no threshold anywhere is written in pmol/L.
The 4.0 ng/mL figure is the part most worth understanding. It is not a diagnostic cut-off and it never was: it is a convention about who is offered further assessment. It misses a meaningful fraction of cancers, and in the Prostate Cancer Prevention Trial about 15 per cent of men with a PSA at or below 4.0 ng/mL who underwent biopsy had prostate cancer, roughly 15 per cent of those being high grade. It also flags a great many men who do not have cancer at all. Age-specific limits — around 2.5 ng/mL at 40 to 49, rising through 3.5 and 4.5 to about 6.5 at 70 to 79 — are widely used to sharpen this, but they are not universally endorsed and no guideline treats them as a rule.
Between 4 and 10 ng/mL sits the grey zone, where the total on its own decides very little. Two derived measures help there. The free-to-total PSA ratio uses the fact that cancer lowers the free fraction, and PSA density divides the total by the prostate volume measured on imaging, which separates a large benign gland from a small gland producing too much. Both are worked out on their own pages, and both need a second number that this converter does not have.
Finally, PSA moves for reasons that have nothing to do with malignancy. Prostatitis and urinary infection can raise it several-fold; so can urinary retention, a catheter, cystoscopy or a recent biopsy, and ejaculation within the previous 48 hours raises it modestly. In the other direction, finasteride and dutasteride roughly halve PSA, so a man on either needs his result doubled before it is compared with any threshold — otherwise a significant level is read as reassuring. None of this is a calculation a page can do for you. The number is one input to a conversation with a clinician who has the examination, the history and, increasingly, an MRI.
Frequently asked questions
How do I convert PSA from ng/mL to pmol/L?
Multiply by 35.1741, a factor derived from a molecular mass of 28,430 daltons. A PSA of 3.2 ng/mL is 112.6 pmol/L. In practice PSA is never reported in molar units; ng/mL, identical to µg/L, is the working unit for every published threshold.
Does a PSA under 4.0 ng/mL mean I do not have prostate cancer?
No. The 4.0 figure is a referral convention rather than a diagnostic cut-off. In the Prostate Cancer Prevention Trial about 15 per cent of men with a PSA at or below 4.0 who were biopsied had cancer, and around 15 per cent of those cancers were high grade. Symptoms and examination findings matter whatever the number.
Does a PSA above 4.0 ng/mL mean I have prostate cancer?
No — most men above the threshold do not. Benign prostatic enlargement, prostatitis, urinary infection, retention, recent instrumentation and ejaculation within 48 hours all raise PSA. A raised result means further assessment, which today usually means examination and MRI before any decision about biopsy.
Should I use age-specific PSA ranges?
They are widely used — roughly 2.5 ng/mL at 40 to 49 rising to about 6.5 at 70 to 79 — because PSA rises with prostate volume and age. They are not universally endorsed: they detect more cancers in younger men and fewer in older men, and no guideline treats them as a rule. Both conventions are offered above.
I take finasteride. Does that change my PSA?
Yes, substantially. Finasteride and dutasteride roughly halve PSA within six to twelve months, so a measured value should be doubled before it is compared with any threshold. A PSA of 3.2 ng/mL on treatment corresponds to roughly 6.4 ng/mL untreated. Tell whoever interprets the result that you are taking it.
Related calculators
References
- Thompson IM, Pauler DK, Goodman PJ, et al. Prevalence of prostate cancer among men with a prostate-specific antigen level ≤4.0 ng per millilitre. N Engl J Med. 2004;350(22):2239–2246.
- Oesterling JE, Jacobsen SJ, Chute CG, et al. Serum prostate-specific antigen in a community-based population of healthy men: establishment of age-specific reference ranges. JAMA. 1993;270(7):860–864.
- Mottet N, van den Bergh RCN, Briers E, et al. EAU-EANM-ESTRO-ESUR-SIOG guidelines on prostate cancer — 2020 update. Eur Urol. 2021;79(2):243–262.