What is free testosterone?
Most testosterone in blood is attached to proteins, mainly SHBG and albumin. Free testosterone is the small part that is not attached, and it is the most readily available to your tissues. A standard total testosterone test cannot tell bound from free.
That is why free testosterone matters in some people and not others. If SHBG is normal, total testosterone is usually a good guide. If SHBG is high (for example with liver disease, an overactive thyroid or estrogen medicines) a normal total can hide a low free level; if SHBG is low (for example with obesity or insulin resistance) a low total can come with a normal free level. The Endocrine Society recommends checking free testosterone when total testosterone is near the lower limit or when a condition that alters SHBG is present.
Free testosterone normal range
| Group | pg/mL | pmol/L | ng/dL |
|---|---|---|---|
| Men 18 and over | 47 to 244 | 163 to 846 | 4.7 to 24.4 |
| Women 18 to 30 | 0.8 to 7.4 | 2.8 to 25.7 | 0.08 to 0.74 |
| Women 31 to 40 | 1.3 to 9.2 | 4.5 to 31.9 | 0.13 to 0.92 |
| Women 41 to 51 | 1.1 to 5.8 | 3.8 to 20.1 | 0.11 to 0.58 |
| Women after menopause | 0.6 to 3.8 | 2.1 to 13.2 | 0.06 to 0.38 |
Ranges are ARUP's, measured by equilibrium dialysis and mass spectrometry. Conversions are ours: 1 pg/mL equals about 3.47 pmol/L or 0.1 ng/dL. Free testosterone units vary more than almost any other lab test, so check whether your report uses pg/mL, ng/dL or pmol/L before comparing.
ARUP Laboratories, equilibrium dialysis. The adult male range is 47 to 244 pg/mL.
Where low starts for men
The European Male Aging Study (3,369 men aged 40 to 79) found sexual symptoms became more likely as free testosterone fell below about 160 to 280 pmol/L (46 to 81 pg/mL). It defined late-onset hypogonadism as at least three sexual symptoms plus total testosterone under 11 nmol/L (about 320 ng/dL) and free testosterone under 220 pmol/L (64 pg/mL). Studies reviewed by the AUA have used free testosterone cut-offs of 4.6 to 7.0 ng/dL (46 to 70 pg/mL).
Calculated vs measured free testosterone
- Equilibrium dialysis is the reference method. It is accurate but slow and expensive.
- Calculated free testosterone uses total testosterone, SHBG and usually albumin in a formula such as Vermeulen's. A 1999 study found calculated values almost identical to equilibrium dialysis, except in pregnancy, and the Endocrine Society accepts an accurate formula.
- Direct "analog" immunoassays give only a fraction of the true value, and the fraction varies with SHBG. The same study found that neither direct assays nor the free androgen index is a reliable index of available testosterone.
What low free testosterone means
Low free testosterone has the same causes as low total testosterone (testicular, pituitary or hypothalamus problems, chronic illness, obesity, sleep apnea, age), plus anything that raises SHBG. MedlinePlus links high SHBG to liver disease, an overactive thyroid, eating disorders and estrogen-containing medicines. Symptoms that track most closely with low levels in the EMAS study were poor morning erections, low sexual desire and erectile dysfunction. If yours is low and you have symptoms, talk to your doctor before considering any treatment.
Worked example: normal total, low-normal free
Say a 55-year-old man with low sexual desire gets a total testosterone of 420 ng/dL, inside ARUP's 300 to 890 ng/dL range for his age, and an SHBG of 80 nmol/L, above ARUP's 19 to 76 nmol/L range for men 50 and over. His calculated free testosterone is 55 pg/mL.
55 pg/mL is inside ARUP's 47 to 244 pg/mL range, but it falls in the 46 to 81 pg/mL zone where the European Male Aging Study saw sexual symptoms become more likely. He does not meet the full EMAS definition of late-onset hypogonadism, which also needs total testosterone under about 320 ng/dL. This is the situation the Endocrine Society means: a normal total can hide a low free level when SHBG is high.
MedlinePlus links high SHBG to liver disease, an overactive thyroid and estrogen medicines. Questions for the doctor: Should we repeat total testosterone and SHBG on a fasting morning sample? Should we check TSH and liver enzymes such as ALT? Is a dialysis free testosterone worth ordering to confirm?
What high free testosterone means
In men, a high free testosterone usually reflects testosterone or anabolic steroid use, or a low SHBG. In women, high testosterone may be caused by PCOS or by adrenal, ovarian or pituitary problems (MedlinePlus). Low SHBG, which MedlinePlus links with obesity, insulin resistance and type 2 diabetes, pushes free testosterone up in both sexes.
How to test free testosterone
- Test between 7 and 10 a.m., fasting, like total testosterone. ARUP specifies a 6 to 10 a.m. collection for its dialysis test.
- Ask for total testosterone and SHBG together, so free testosterone can be calculated.
- Avoid direct analog free testosterone tests.
- Repeat a low result before acting on it.
Common questions about free testosterone
Is the free androgen index the same thing?
No. The free androgen index is total testosterone divided by SHBG, times 100. The 1999 Vermeulen study found it is not a reliable index of available testosterone, so a calculated free testosterone from a validated formula is the better number for men. Our free androgen index page covers how it is reported.
What should be tested with it?
Total testosterone and SHBG from the same morning draw, since the calculation needs both, plus albumin if your lab uses it in the formula. If free testosterone is low, the usual next tests are LH and prolactin to find the cause, as the testosterone page explains.
Why do women get a different range?
Women make far less testosterone, and ARUP's female ranges also change with age: the upper limit is 9.2 pg/mL at 31 to 40 but 3.8 pg/mL after menopause. For women the test is mostly used to look into signs of too much testosterone, such as with PCOS (MedlinePlus).
Which at-home tests include free testosterone
SiPhox Health reports calculated free testosterone, not a dialysis measurement. It appears on Longevity Essentials (men), Hormone Focus (men and women, with % free testosterone, albumin and the free androgen index), Ultimate 360 and GLP Optimization. Women who want free testosterone, for example to look at PCOS, need Hormone Focus or Ultimate 360; our hormone test guide for women explains the options. Men can compare kits in the at-home testosterone test guide.
A note on home samples: SiPhox's partner lab tests capillary blood collected from the upper arm. SiPhox says its results show a 95% to 99% correlation with venous draws in its own quarterly comparisons against Labcorp and Quest, but it has not published a study of the EasyDraw device. If a result would change a treatment decision, confirm it with a venous test through your doctor.
Longevity Essentials
The default panel: heart, metabolic, hormone and inflammation markers in one draw.
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Hormone Focus
Sex hormones for men and women, including PSA for men and progesterone for women.
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Ultimate 360
Everything on the four core panels plus iron studies, B12 and folate, GGT and PSA.
Check priceFrequently asked questions
What is a normal free testosterone level for a man?
About 47 to 244 pg/mL (4.7 to 24.4 ng/dL, or roughly 163 to 846 pmol/L) on ARUP's equilibrium dialysis test for men 18 and over. Other labs and methods use different ranges and units.
What free testosterone level is too low?
There is no single cut-off. The European Male Aging Study used under 220 pmol/L (64 pg/mL) plus low total testosterone and three sexual symptoms to define late-onset hypogonadism. Your doctor will weigh symptoms and repeat tests.
What is a normal free testosterone level for a woman?
ARUP gives 0.8 to 7.4 pg/mL at 18 to 30, 1.3 to 9.2 pg/mL at 31 to 40, 1.1 to 5.8 pg/mL at 41 to 51 and 0.6 to 3.8 pg/mL after menopause.
Is calculated free testosterone accurate?
Yes, when it uses a validated formula with good total testosterone and SHBG measurements. Calculated values closely match equilibrium dialysis except in pregnancy. Direct analog immunoassays are not reliable.
Sources
- ARUP Laboratories Test Directory: Testosterone, free, by dialysis and mass spectrometry
- ARUP Laboratories Test Directory: Testosterone, free and total, with SHBG (females)
- Bhasin S et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 2018
- Wu FC et al. Identification of late-onset hypogonadism in middle-aged and elderly men (European Male Aging Study). N Engl J Med 2010
- Vermeulen A et al. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab 1999
- ARUP Laboratories Test Directory: Sex hormone binding globulin
- ARUP Laboratories Test Directory: Testosterone (adult males)
- American Urological Association: Evaluation and management of testosterone deficiency guideline
- MedlinePlus Lab Tests: Testosterone levels test
- MedlinePlus Lab Tests: SHBG blood test
- SiPhox Health: panel comparison (checked 29 Sep 2026)
- SiPhox Health: Hormone Focus panel