Free testosterone pg/mL to pmol/L Converter

Free testosterone in two units: the short answer

To convert free testosterone from pg/mL to pmol/L, multiply by 3.467. To convert pmol/L back to pg/mL, divide by 3.467 (or multiply by 0.2884). A value of 65 pg/mL is therefore about 225 pmol/L, and 300 pmol/L is about 87 pg/mL. The converter above works in both directions and shows typical laboratory ranges for adult men and women.

Free testosterone is reported in a wider variety of units than almost any other hormone: pg/mL, pmol/L, ng/dL, ng/L and sometimes nmol/L. On top of that, it can be measured directly, measured by dialysis, or calculated from total testosterone, SHBG and albumin – and those approaches give different numbers. This guide explains each of these, so you can convert a result correctly and know whether two results are actually comparable.

What free testosterone is

Only about 1–3% of the testosterone in the blood is "free" – not attached to any protein. The rest is bound either tightly to sex hormone-binding globulin (SHBG) or loosely to albumin. Free testosterone is the fraction that can enter cells and act on androgen receptors, so in theory it is the best reflection of testosterone activity in the body.

The free fraction matters most when SHBG is abnormal. Two men can have identical total testosterone yet very different free levels:

• A man with high SHBG (common with ageing, hyperthyroidism, liver disease, HIV or some anticonvulsants) may have a normal total testosterone but a low free level.
• A man with low SHBG (common with obesity, type 2 diabetes, hypothyroidism or nephrotic syndrome) may have a low total testosterone but a normal free level.

For this reason the Endocrine Society recommends measuring or calculating free testosterone when total testosterone is near the lower limit of normal or when conditions that alter SHBG are present. In women, free testosterone or the free androgen index is the preferred marker of androgen excess in polycystic ovary syndrome.

"Bioavailable testosterone" is a related term: free testosterone plus the albumin-bound fraction. It is reported in ng/dL or nmol/L and has much higher values than free testosterone. Do not compare a bioavailable result with a free testosterone range.

How free testosterone is measured

Equilibrium dialysis (the reference method)

A sample is placed on one side of a membrane that lets only unbound hormone pass. After equilibrium, the free testosterone on the other side is measured, ideally by LC-MS/MS. This is the most accurate method but is expensive and offered by relatively few laboratories.

Calculated free testosterone

Most laboratories calculate free testosterone from total testosterone, SHBG and albumin, usually using the Vermeulen equation (1999). The calculation uses the binding affinities of testosterone for SHBG and albumin and agrees reasonably well with dialysis in most people. Its accuracy depends on the accuracy of the total testosterone and SHBG measurements. Many laboratories assume a standard albumin of 4.3 g/dL if albumin is not measured.

Direct analog immunoassays

Some laboratories once used "direct" or "analog" free testosterone immunoassays. These are known to be inaccurate – they give values much lower than dialysis and are affected by SHBG – and the Endocrine Society advises against using them. If your report shows a very low free testosterone in pg/mL from an analog assay, its reference range will also be much lower, and the numbers cannot be converted meaningfully to a dialysis-based range.

Free androgen index (FAI)

The FAI is 100 × total testosterone (nmol/L) ÷ SHBG (nmol/L). It is a ratio, has no unit, and is mainly used in women. It is unreliable in men because SHBG binding becomes saturated at male testosterone levels.

pg/mL, pmol/L and the other units

• pg/mL (picograms per milliliter) – common in US reports. Numerically identical to ng/L.
• pmol/L (picomoles per liter) – the SI unit, common in UK, European and Australian reports.
• ng/dL – used by some US laboratories for calculated free testosterone. 1 ng/dL = 10 pg/mL.
• nmol/L – occasionally used; 1 nmol/L = 1,000 pmol/L.

Why the factor is 3.467

Testosterone's molar mass is 288.4 g/mol. One picomole weighs 288.4 pg. A concentration of 1 pg/mL equals 1,000 pg per liter, which is 1,000 ÷ 288.4 = 3.467 pmol/L. This is the same molecule and factor as for total testosterone, just at a smaller scale.

How to convert free testosterone step by step

1. Identify the unit. If it is ng/dL, multiply by 10 to get pg/mL. If it is nmol/L, multiply by 1,000 to get pmol/L.
2. From pg/mL, multiply by 3.467 to get pmol/L.
3. From pmol/L, divide by 3.467 to get pg/mL.
4. Round to whole numbers for men; keep one decimal place for women's values.

Worked examples

• 50 pg/mL × 3.467 = 173 pmol/L – the lower end of a typical adult male range.
• 100 pg/mL × 3.467 = 347 pmol/L.
• 210 pg/mL × 3.467 = 728 pmol/L – the upper end of a typical adult male range.
• 225 pmol/L ÷ 3.467 = 64.9 pg/mL, often cited as a lower limit for free testosterone in men.
• 6.5 ng/dL = 65 pg/mL × 3.467 = 225 pmol/L.
• 0.25 nmol/L = 250 pmol/L ÷ 3.467 = 72 pg/mL.
• 3.0 pg/mL × 3.467 = 10.4 pmol/L – within a typical range for adult women.

Mental shortcut

Multiply pg/mL by 3.5 or divide pmol/L by 3.5. For 80 pg/mL: 80 × 3.5 = 280 pmol/L (exact: 277).

Free testosterone conversion chart

Typical free testosterone ranges

These ranges are illustrative only. Free testosterone ranges vary more between laboratories than almost any other routine test, because of the different methods described above. Always use the range printed on your own report, and make sure it was derived using the same method as your result.

Adult men

With equilibrium dialysis or calculated methods, typical adult male ranges are roughly 50–210 pg/mL (175–730 pmol/L). Thresholds suggested for low free testosterone include:

• about 65 pg/mL (225 pmol/L), used in several European studies and the European Male Ageing Study analyses;
• about 50 pg/mL (175 pmol/L), which corresponds to the lower end of many laboratory ranges.

The Endocrine Society does not specify a single cut-off; it recommends using the lower limit of the normal range from a laboratory that uses equilibrium dialysis or a validated calculation.

Adult women

Typical ranges for women are about 0.3–6.4 pg/mL (1–22 pmol/L), varying with age and method. Free testosterone falls gradually with age in women and is lower after menopause. Raised levels are most commonly due to PCOS; markedly raised levels need investigation for other causes.

Effect of age in men

Free testosterone falls more steeply with age than total testosterone, because SHBG rises with age. An 80-year-old man may have a total testosterone similar to a 30-year-old but a free testosterone 40–50% lower. Some laboratories provide age-adjusted ranges, but whether low free testosterone in older men without other signs of disease should be treated remains debated.

Comparing calculated and measured results

If you have one result from dialysis and one calculated, expect differences of 10–20%, sometimes more. Different calculation formulas (Vermeulen, Södergard, Emadi-Konjin and others) also give slightly different values from the same inputs. When you track free testosterone over time, use the same laboratory and method.

If your report gives total testosterone and SHBG but not free testosterone, a clinician can calculate it. Free testosterone calculators are widely available, but they need both values in the correct units – total testosterone in nmol/L and SHBG in nmol/L – which is where the total testosterone converter on this site can help.

What affects free testosterone results

• Time of day – like total testosterone, free testosterone is highest in the morning. Test between 7 and 10 a.m.
• Fasting – a fasting sample is preferred, as meals can lower testosterone.
• SHBG-altering conditions – obesity, insulin resistance, hypothyroidism and nephrotic syndrome lower SHBG; ageing, hyperthyroidism, liver cirrhosis, HIV, oestrogen therapy and anticonvulsants raise it.
• Hormonal contraceptives and oral oestrogen raise SHBG and lower free testosterone in women.
• Albumin – very low albumin (for example in serious illness) affects calculated values.
• Acute illness, sleep loss, extreme exercise and calorie restriction lower testosterone temporarily.
• Medicines – opioids, glucocorticoids and androgen-suppressing drugs lower levels; testosterone therapy raises them depending on dose timing.
• Biotin can affect some immunoassays used for total testosterone and SHBG, and therefore calculated free testosterone.

A worked example of SHBG's effect

Consider two 55-year-old men, both with a total testosterone of 12 nmol/L (346 ng/dL) and a normal albumin of 4.3 g/dL:

• Man A has obesity and type 2 diabetes, with an SHBG of 20 nmol/L. His calculated free testosterone (Vermeulen) is roughly 310 pmol/L (about 89 pg/mL) – comfortably within a typical range.
• Man B is lean and has mild hyperthyroidism, with an SHBG of 70 nmol/L. His calculated free testosterone is roughly 140 pmol/L (about 41 pg/mL) – below many laboratories' lower limit.

Same total testosterone, very different free testosterone. This is exactly the situation in which the Endocrine Society recommends looking beyond the total value. The approach also applies in reverse: an obese man with a low total testosterone may have a normal free level, and losing weight raises both SHBG and total testosterone.

Free testosterone and testosterone therapy

When men take testosterone treatment, monitoring is usually based on total testosterone, because it is cheaper and more standardised. Free testosterone may be helpful when SHBG is markedly abnormal. Oral oestrogens and some other medicines change SHBG during treatment, which can make total testosterone rise or fall without a matching change in the free level.

Reading a report that gives several testosterone values

Many reports now list total testosterone, SHBG, albumin and calculated free testosterone together, sometimes with bioavailable testosterone and a free androgen index. A sample report might read:

• Total testosterone: 14.2 nmol/L (410 ng/dL)
• SHBG: 48 nmol/L
• Albumin: 44 g/L (4.4 g/dL)
• Calculated free testosterone: 245 pmol/L (71 pg/mL)
• Bioavailable testosterone: 6.0 nmol/L (173 ng/dL)

All of these are consistent with each other: the free fraction here is about 1.7% of the total, which is typical. If you see a free testosterone that seems out of proportion – for example, a free value of 2.5% or more with a normal SHBG – check whether the units have been mixed up, such as pg/mL being read as pmol/L. Converting each value into one system is the quickest way to spot such errors.

Free testosterone in women: practical notes

In women, free testosterone levels are low enough that method choice matters even more than in men. The international PCOS guideline recommends calculated free testosterone, the free androgen index or calculated bioavailable testosterone as first-line tests of biochemical androgen excess, and suggests using high-quality assays such as LC-MS/MS for total testosterone when available. Direct free testosterone immunoassays are specifically discouraged.

Hormonal contraception changes the picture: combined oral contraceptives raise SHBG, often substantially, which lowers free testosterone. For this reason, testing for androgen excess is usually done off hormonal contraception for at least three months where that is safe and practical. A woman with symptoms of androgen excess and a normal free testosterone while taking the pill may still have PCOS.

When free testosterone is worth testing

Common reasons a clinician orders free testosterone include:

• total testosterone in the borderline-low range (roughly 200–400 ng/dL, 7–14 nmol/L) in a man with symptoms
• conditions that alter SHBG, such as obesity, diabetes, thyroid or liver disease, or older age
• monitoring some men on testosterone therapy
• evaluating signs of androgen excess in women, such as hirsutism, acne or irregular periods

When to see a doctor

See a doctor if you are a man with symptoms of low testosterone – reduced sexual desire, erectile problems, loss of body hair, breast enlargement, fatigue or low mood – and your free testosterone is below your laboratory's range on a morning sample. A low result should be confirmed and followed by tests of LH, FSH and often prolactin. Women with free testosterone above the laboratory range, especially with rapidly progressing hair growth, voice change or increasing muscle mass, should be assessed promptly.