Testosterone Calculator

Q: What is a normal free testosterone level for men?

Most healthy adult men fall between 50 and 210 pg/mL (about 0.2 to 0.6 nmol/L, or 5 to 21 ng/dL). The 2017 BSSM guidelines treat 0.225 nmol/L (about 65 pg/mL) as a low cut-off. Below that, low testosterone symptoms are more likely. Ranges differ a little from lab to lab, so always check the range printed on your own report.

Q: How do you convert testosterone from ng/dL to nmol/L?

Multiply ng/dL by 0.03467 to get nmol/L. To go the other way, multiply nmol/L by 28.84 . 500 ng/dL × 0.03467 = 17.3 nmol/L 17.3 nmol/L × 28.84 = 500 ng/dL For free testosterone in pg/mL, multiply nmol/L by 288.43 .

Q: What is a normal SHBG level?

For adult men, SHBG usually runs about 10 to 57 nmol/L . For women it is higher, often 18 to 144 nmol/L , and it rises a lot during pregnancy or on birth control pills. SHBG is always reported in nmol/L, so there is no unit to convert.

Q: What lowers SHBG?

SHBG drops with obesity, insulin resistance, type 2 diabetes, an underactive thyroid, and anabolic steroid use . High insulin is the biggest driver. Low SHBG leaves a larger share of testosterone free, but it also often signals a metabolic problem worth checking with your doctor.

Introduction

Your blood test shows total testosterone, but that number does not tell the whole story. Most testosterone in your blood is stuck to proteins. Only the loose part can reach your cells and do its job. This calculator works out how much of your testosterone is that loose part.

Enter three lab values: total testosterone, SHBG, and albumin. The tool then shows your free testosterone (not bound to anything) and your bioavailable testosterone (free plus the part loosely held by albumin). You can see the results in pg/mL, ng/dL, or nmol/L.

The math uses the Vermeulen method, the formula most clinics and labs use. The calculator also shows each step, a chart of how your testosterone is split up, and how your free level would change if your SHBG went up or down.

High SHBG can hide low free testosterone, even when your total number looks fine. Seeing the split makes your lab report easier to read. Then talk with your doctor about what the numbers mean for you.

How to use our Testosterone Calculator

Enter three numbers from your blood test (total testosterone, SHBG, and albumin) and the calculator shows your free testosterone and bioavailable testosterone, plus how much of your testosterone is bound to SHBG and albumin.

Total Testosterone: Type the total testosterone number from your lab report, then pick the unit your lab used (ng/dL, ng/mL, nmol/L, nmol/dL, or nmol/mL). This is the starting value for the whole calculation.

SHBG: Type your sex hormone-binding globulin level. Labs report SHBG in nmol/L, so no unit choice is needed. SHBG holds testosterone tightly, so a high number lowers your free testosterone.

Albumin: Type your albumin level and pick g/dL or g/L. If you do not know it, leave the default of 4.3 g/dL (43 g/L), which is the normal adult value used in most free testosterone calculators.

Display unit (Free Testosterone): Choose pg/mL, nmol/L, or ng/dL for your free testosterone result. Pick the same unit your doctor or lab uses so the numbers are easy to compare.

Display unit (Bioavailable Testosterone): Choose pg/mL, nmol/L, or ng/dL for your bioavailable testosterone result. This also changes the units in the albumin-bound and SHBG-bound boxes.

Click Calculate to see your results, the step-by-step math using the Vermeulen formula, a chart of your binding breakdown, and a graph showing how SHBG changes your free testosterone. Click Reset to go back to the sample values.

What Is Free and Bioavailable Testosterone?

Testosterone travels in your blood in three forms. Most of it sticks tightly to a protein called SHBG (sex hormone-binding globulin). Some of it sticks loosely to albumin, another blood protein. A small part floats free and is not stuck to anything at all.

Only the loose and free parts can enter your cells and do work. That is why doctors look at these numbers:

Free testosterone is the part not bound to any protein, usually about 1% to 3% of your total.
Bioavailable testosterone is free testosterone plus the albumin-bound part. This is the share your body can actually use.
SHBG-bound testosterone is locked up tight and not available to your cells.

Why Total Testosterone Alone Can Fool You

Two men can have the same total testosterone but feel very different. If one has high SHBG, more of his hormone is locked away, so he may have low energy, low sex drive, or other low-T signs even though his lab report looks "normal." If SHBG is low, more testosterone stays free, and his usable level may be fine even with a lower total.

Things that raise SHBG include getting older, thyroid problems, liver disease, and estrogen. Things that lower SHBG include obesity, insulin resistance, type 2 diabetes, and steroid use.

The Vermeulen Method

This tool uses the Vermeulen equation, published in 1999 in the Journal of Clinical Endocrinology & Metabolism. It is the most used formula in clinics and research. It takes your total testosterone, SHBG, and albumin, then uses known binding strengths to solve for how much hormone stays free. Measuring free testosterone directly in a lab is costly and often not accurate, so this math method is the common choice.

What the Numbers Mean

The 2017 British Society for Sexual Medicine (BSSM) guidelines use 0.225 nmol/L (about 65 pg/mL) of free testosterone as a cut-off. Below that, low testosterone symptoms are more likely. Typical adult male ranges run near 0.2 to 0.6 nmol/L (about 50 to 210 pg/mL) free, and bioavailable testosterone is often 30% to 55% of total.

Lab Tips

Draw your blood in the morning, usually before 10 a.m., since testosterone peaks early in the day. Fast if your doctor asks. Test twice on separate days before making any choices, because levels move a lot day to day. If you do not know your albumin, the default of 4.3 g/dL (43 g/L) is the standard value used by most labs.

Note: These results are an estimate, not a diagnosis. Talk with a doctor or endocrinologist about your symptoms and your full lab panel before starting any treatment.

Formulas used

Total testosterone unit conversion to nmol/L

T_{total}(\text{nmol/L}) = T_{input} \times f_{unit}, \quad f_{\text{ng/dL}} = 0.03467,\; f_{\text{ng/mL}} = 3.467,\; f_{\text{nmol/dL}} = 10,\; f_{\text{nmol/mL}} = 1000

Albumin molar concentration

[Alb] = \frac{Alb\ (\text{g/L})}{66{,}500\ \text{g/mol}}

Albumin binding term (alpha)

\alpha = K_a\,[Alb], \quad K_a = 3.6\times 10^{4}\ \text{L/mol}

Vermeulen quadratic coefficients

a = K_t(1+\alpha), \quad b = (1+\alpha) + K_t\left([SHBG] - [T]\right), \quad c = -[T], \quad K_t = 1.0\times 10^{9}\ \text{L/mol}

Free testosterone (Vermeulen 1999)

[T_{free}] = \frac{-b + \sqrt{b^2 - 4ac}}{2a}

Bioavailable testosterone

T_{bio} = T_{free}\,(1+\alpha)

Albumin-bound and SHBG-bound testosterone

T_{alb} = T_{bio} - T_{free}, \quad T_{SHBG} = T_{total} - T_{bio}

Output unit conversion from nmol/L

T(\text{pg/mL}) = T_{\text{nmol/L}} \times 288.43, \quad T(\text{ng/dL}) = T_{\text{nmol/L}} \times \frac{288.43}{10}

Frequently asked questions

What is a normal free testosterone level for men?

Most healthy adult men fall between 50 and 210 pg/mL (about 0.2 to 0.6 nmol/L, or 5 to 21 ng/dL). The 2017 BSSM guidelines treat 0.225 nmol/L (about 65 pg/mL) as a low cut-off. Below that, low testosterone symptoms are more likely. Ranges differ a little from lab to lab, so always check the range printed on your own report.

What is a normal free testosterone level for women?

Women have far less testosterone than men. Total testosterone usually runs about 15 to 70 ng/dL, and free testosterone is often under 5 pg/mL. High free testosterone in women can point to PCOS, especially when SHBG is low. Ranges vary by lab and by age, so compare your number with your own report.

How do you convert testosterone from ng/dL to nmol/L?

Multiply ng/dL by 0.03467 to get nmol/L. To go the other way, multiply nmol/L by 28.84.

500 ng/dL × 0.03467 = 17.3 nmol/L
17.3 nmol/L × 28.84 = 500 ng/dL

For free testosterone in pg/mL, multiply nmol/L by 288.43.

What is a normal SHBG level?

For adult men, SHBG usually runs about 10 to 57 nmol/L. For women it is higher, often 18 to 144 nmol/L, and it rises a lot during pregnancy or on birth control pills. SHBG is always reported in nmol/L, so there is no unit to convert.

Can total testosterone be normal but free testosterone low?

Yes, and it is common. If SHBG is high, more of your hormone is locked to that protein and cannot reach your cells. Your total number can look fine while your free number sits below the cut-off. This is why doctors check SHBG along with total testosterone when symptoms do not match the lab report.

What causes high SHBG?

Common causes include:

Getting older (SHBG rises about 1% per year after 40)
Overactive thyroid
Liver disease, such as cirrhosis or hepatitis
High estrogen, birth control pills, or pregnancy
Anti-seizure drugs
Very low body fat, heavy endurance training, or long fasting

What lowers SHBG?

SHBG drops with obesity, insulin resistance, type 2 diabetes, an underactive thyroid, and anabolic steroid use. High insulin is the biggest driver. Low SHBG leaves a larger share of testosterone free, but it also often signals a metabolic problem worth checking with your doctor.

What are the symptoms of low free testosterone?

Common signs include:

Low sex drive and weak erections
Tiredness even after sleep
Loss of muscle and gain of belly fat
Low mood, irritability, or brain fog
Poor workout recovery

These signs have many other causes too. Two morning blood tests on separate days are needed before any diagnosis.

Is free testosterone more important than total testosterone?

Neither one stands alone. Total testosterone is the starting point and works fine when SHBG is normal. Free testosterone matters more when SHBG is high or low, when you are older, or when you are obese, since those situations shift how much hormone stays usable. Doctors read both together with your symptoms.

How does albumin affect bioavailable testosterone?

Albumin holds testosterone loosely, so that part still counts as usable. If albumin is low, from liver or kidney disease or poor nutrition, less hormone is carried this way and bioavailable testosterone drops. Free testosterone barely moves. A normal adult value of 4.3 g/dL (43 g/L) is used when albumin is not measured.

What is the free androgen index and how is it different?

The free androgen index (FAI) is a quick ratio: (total testosterone in nmol/L ÷ SHBG in nmol/L) × 100. It ignores albumin and gives a percentage, not a real hormone level. It is used most often in women to screen for PCOS. The Vermeulen equation is more exact for men because it accounts for albumin binding.

How much does free testosterone drop with age?

Total testosterone falls about 1% per year after age 30 to 40. At the same time SHBG rises about 1% per year, so free testosterone falls faster, closer to 2% to 3% per year. That is why an older man can have a normal-looking total number and still feel the effects of low testosterone.

Can losing weight raise free testosterone?

Yes. Body fat turns testosterone into estrogen and drives insulin resistance, which pushes SHBG down and total testosterone down. Losing weight often raises both total and free testosterone. Better sleep, strength training, and treating sleep apnea help too.

Why do doctors calculate free testosterone instead of measuring it?

The gold-standard lab method, equilibrium dialysis, is slow and costly and few labs offer it. The cheap direct analog assay gives poor results. Calculating free testosterone from total testosterone, SHBG, and albumin is fast, cheap, and matches dialysis results closely, so clinics use it as the practical choice.

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