Last updated: June 2026
Free Testosterone Calculator
Quick answer: With a total testosterone of 600 ng/dL (about 20.8 nmol/L), SHBG of 40 nmol/L and albumin of 4.3 g/dL, calculated free testosterone is about 115 pg/mL (~1.9% of total) and bioavailable testosterone about 270 ng/dL — broadly normal for adult men. This calculator uses the Vermeulen equation, the validated method for estimating free testosterone from a standard blood panel.
About this calculator
This free testosterone calculator estimates your free and bioavailable testosterone from three blood values — total testosterone, SHBG, and albumin — using the Vermeulen (1999) equation. Unlike the simpler Free Androgen Index (FAI), which is only a ratio proxy, the Vermeulen method models how testosterone binds to SHBG and albumin and returns an actual free-T value in pg/mL. If you are on Testosterone (TRT) and need your injection draw volume instead, use the Testosterone (TRT) dosage calculator. Free, instant, no login.
The formula
Free testosterone (FT) is the physiological root of this quadratic, where T and SHBG are converted to mol/L, N = 1 + Ka · albumin, Ka = 3.6×10⁴ L/mol (albumin binding), and Kt = 1.0×10⁹ L/mol (SHBG binding). Bioavailable testosterone = N × FT — the free fraction plus the loosely albumin-bound fraction. US labs report total testosterone in ng/dL (the calculator converts it) and SHBG in nmol/L.
How to use this calculator
You need two values from a blood test: your total testosterone and your SHBG, both standard markers on a hormone panel. Albumin is the third input — most panels don't include it, so the calculator defaults to 4.3 g/dL, the standard population value; enter your own only if you have it. US labs report total testosterone in ng/dL (select ng/dL) and SHBG in nmol/L.
To convert total testosterone manually, divide ng/dL by 28.84 to get nmol/L (e.g. 600 ng/dL ÷ 28.84 = 20.8 nmol/L). US labs typically report ng/dL, while UK, Australian and New Zealand labs report nmol/L. The result updates the moment you enter total T and SHBG.
Worked example
Total testosterone: 600 ng/dL (20.8 nmol/L)
SHBG: 40 nmol/L · Albumin: 4.3 g/dL (default)
Free testosterone ≈ 115 pg/mL (~1.9% of total) · bioavailable ≈ 270 ng/dL
Total testosterone: 650 ng/dL (22.5 nmol/L, appears normal)
SHBG: 80 nmol/L (elevated) · Albumin: 4.3 g/dL
Free testosterone ≈ 75 pg/mL (~1.2% of total) — low despite a normal total T
Interpreting your result
Reference ranges vary between laboratories. Broadly, calculated free testosterone for adult men:
| Free testosterone | General interpretation |
|---|---|
| Below 50 pg/mL | Low — below the typical adult-male range |
| 50 – 210 pg/mL | Broadly normal range for adult men |
| Above 210 pg/mL | Elevated — discuss with your doctor |
Reference ranges vary between laboratories and by age and assay. The 50–210 pg/mL range is a broad population estimate for adult men — always interpret your result alongside your specific laboratory's reference range and in consultation with your doctor.
Method per Vermeulen A, et al. J Clin Endocrinol Metab. 1999;84(10):3666–72. Individual lab ranges may vary — verify with your prescribing clinician.
A low free or bioavailable testosterone alongside a normal total testosterone often points to elevated SHBG binding up a large share of your testosterone — which can be clinically relevant even when total T looks adequate. The reverse (low SHBG) can make free T relatively high.
Always discuss your results in context with your doctor or endocrinologist — calculated free testosterone is one data point, not a standalone diagnosis.
Frequently asked questions
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How this is calculated
Free testosterone is estimated with the Vermeulen (1999) equation from total testosterone, SHBG and albumin; bioavailable testosterone is the free fraction plus the albumin-bound fraction. It runs entirely in your browser — nothing is stored — and is an interpretive aid, not medical advice. Discuss results with your prescriber.