Testosterone Calculator

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 lowers SHBG?

SHBG drops with obesity, insulin resistance, type 2 diabetes, an underactive thyroid, and androgen use . 2 In obesity and diabetes, the low SHBG is most likely due to low-grade inflammation and fat in the liver rather than high insulin. 2 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 most widely used formula in research and commercial labs.² 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), the same default our free testosterone calculator uses.

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 4% of your total.²
Bioavailable testosterone is free testosterone plus the albumin-bound part.² 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, an overactive thyroid, advanced liver disease, and high estrogen.² Things that lower SHBG include obesity, insulin resistance, type 2 diabetes, and androgen use.²

The Vermeulen Method

This tool uses the Vermeulen equation, published in 1999 in the Journal of Clinical Endocrinology & Metabolism.¹ It is the most widely used formula in research and commercial labs.² It takes your total testosterone, SHBG, and albumin, then uses known binding strengths to solve for how much hormone stays free. Measuring free testosterone by equilibrium dialysis is too slow for routine use, and the quick direct assay is not reliable.¹ That is why this math method is the common choice.

What the Numbers Mean

This calculator compares your free testosterone with 0.225 nmol/L (about 65 pg/mL). In a large European study of aging men, sexual symptoms were linked with free testosterone below 220 pmol/L together with total testosterone below 11 nmol/L.² Reference ranges differ from lab to lab, so check the range on your own report.

Lab Tips

The Endocrine Society recommends testing fasting morning total testosterone and repeating the morning test to confirm a low result.³ If you do not know your albumin, this calculator uses 4.3 g/dL (43 g/L).

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) ²

\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?

It depends on the lab and on age. In a large European study of aging men, sexual symptoms were linked with free testosterone below 220 pmol/L together with total testosterone below 11 nmol/L.² This calculator flags free testosterone below 0.225 nmol/L (about 65 pg/mL). 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. For total testosterone, MedlinePlus lists 8.4 to 48.1 ng/dL for women aged 17 to 50 and 2.9 to 40.1 ng/dL over 50.⁴ 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?

Ranges vary from lab to lab, so use the range on your own report. Pregnancy and birth control pills raise SHBG.² SHBG is usually reported in nmol/L.

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, an overactive thyroid, advanced liver disease and hepatitis C, high estrogen (as with birth control pills or pregnancy), anti-seizure drugs, and extreme weight loss.²

What lowers SHBG?

SHBG drops with obesity, insulin resistance, type 2 diabetes, an underactive thyroid, and androgen use.² In obesity and diabetes, the low SHBG is most likely due to low-grade inflammation and fat in the liver rather than high insulin.² 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. The Endocrine Society recommends confirming a low result with a repeat fasting morning test before diagnosis.³

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. The Endocrine Society recommends a free testosterone test when total testosterone is near the lower limit of normal or a condition alters SHBG.³ 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. This calculator uses 4.3 g/dL (43 g/L) 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) × 100.¹ It ignores albumin and gives a percentage, not a real hormone level. It is used most often in women to screen for PCOS. In Vermeulen's comparison, the FAI was not a reliable index of bioavailable testosterone, while the calculated value was.¹

How much does free testosterone drop with age?

Testosterone production declines steadily with age in men, and more than 20% of healthy men over 60 have levels below the range for young men.⁵ SHBG also rises with age, so free testosterone falls faster than total.² 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?

Often, yes. Obesity is one of the conditions linked with low SHBG.² 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 quick direct analog assay is not reliable.¹ In Vermeulen's study, free testosterone calculated from total testosterone and SHBG was almost identical to dialysis results, except in pregnancy.¹ That makes it the practical choice.

Sources

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