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Total T4 in two units: the short answer
To convert total t4 from µg/dL to nmol/L, multiply by 12.87. To go back from nmol/L to µg/dL, multiply by 0.0777 (or divide by 12.87). For example, 9 µg/dL × 12.87 = 116 nmol/L. The converter above works in both directions and shows where the result sits against typical reference ranges.
What the test measures
Total T4 measures all thyroxine in the blood, bound and free. US labs report it in µg/dL (mcg/dL); SI labs use nmol/L. Thyroxine's molar mass is 776.9 g/mol, so 1 µg/dL = 12.87 nmol/L.
Why the units differ
Total T4 is less used than free T4 today because binding-protein changes (pregnancy, oral estrogen) shift it without changing thyroid status. When an older or US report lists total T4, conversion lets you compare it with SI-unit ranges.
Where the factor comes from
The conversion factor comes from the molar mass (776.87 g/mol) and the volume units on each side. Laboratories may round the factor slightly differently, which can change the last digit but never the clinical meaning.
How to convert step by step
- Check the unit printed next to the result on your report – µg/dL or nmol/L.
- µg/dL → nmol/L: multiply by 12.87.
- nmol/L → µg/dL: multiply by 0.0777.
- Round to the same number of decimals your lab uses.
Worked example in reverse: 64.0 nmol/L × 0.0777 = 5.0 µg/dL.
Total T4 conversion chart
| µg/dL | nmol/L |
|---|---|
| 3 | 39 |
| 4 | 51 |
| 5 | 64 |
| 6 | 77 |
| 7 | 90 |
| 8 | 103 |
| 9 | 116 |
| 10 | 129 |
| 11 | 142 |
| 12 | 154 |
| 13 | 167 |
| 15 | 193 |
| nmol/L | µg/dL |
|---|---|
| 39 | 3 |
| 51 | 4 |
| 64 | 5 |
| 77 | 6 |
| 90 | 7 |
| 103 | 8 |
| 116 | 9 |
| 129 | 10 |
| 142 | 11 |
| 154 | 12 |
| 167 | 13 |
| 193 | 15 |
Total T4 levels: what the numbers mean
| Category | µg/dL | nmol/L |
|---|---|---|
| Typical adult rangeAbout 64–154 nmol/L; varies by lab | 5 – 12 | 64 – 154 |
Typical adult range. Pregnancy and estrogen raise total T4 through higher thyroid-binding globulin.
Typical adult range. Pregnancy and estrogen raise total T4 through higher thyroid-binding globulin.
Interpreting total t4 results
Because more than 99.9% of T4 travels bound to proteins, anything that changes those proteins changes total T4. Pregnancy, birth-control pills and hepatitis raise thyroxine-binding globulin and push total T4 up; nephrotic syndrome, androgens and serious illness pull it down. That is why most clinicians now order TSH with free T4, and use total T4 mainly in specific settings.
A single result outside the reference range is common and often not significant on its own. Reference ranges are set so that about 1 in 20 healthy people fall outside them, and every laboratory sets its own limits for its method. Use the range printed on your report and discuss results with the clinician who ordered the test.
When to see a doctor
Contact your clinician if a result is flagged as abnormal and you have symptoms, if a value is far outside the range, or if results are changing over time. This page explains units; it cannot diagnose or replace medical advice.
Frequently asked questions
What is 100 nmol/L total T4 in µg/dL?
100 ÷ 12.87 = 7.8 µg/dL.
Is total T4 the same as free T4?
No. Free T4 is the unbound fraction (about 0.03%) and uses different units (ng/dL or pmol/L). Use our free T4 converter for those.
Can I use this converter for any lab?
Yes for the unit conversion, which is fixed by chemistry. Reference ranges differ between labs and methods, so compare your converted value with your own lab's range.