Free T4 (fT4) ng/dL → pmol/L
Convert free t4 (ft4) from ng/dL to pmol/L
Sources last checked: 2026-11-03
Free T4 (fT4) ng/dL → pmol/L
Convert free t4 (ft4) from ng/dL to pmol/L
Converts units only; reference ranges depend on the laboratory, the assay and the patient.
What is the Free T4 (fT4) ng/dL → pmol/L?
Free thyroxine (fT4) is reported in ng/dL in the USA, Turkey and many German and Austrian laboratories, and in pmol/L in the UK, Scandinavia and most SI-based literature. This converter multiplies by 12.87, the factor in the AMA Manual of Style SI table, which follows from the molar mass of thyroxine (776.87 g/mol). It converts the free hormone only, not total T4.
When to use it
- Reading a UK, Scandinavian or SI-based guideline or paper that quotes fT4 in pmol/L
- Comparing a result from a lab that reports ng/dL with an earlier result in pmol/L
- Documenting thyroid function for a colleague or registry that expects SI units
- Exam questions and case reports written in SI units
When not to use it
- Total T4, which is reported in µg/dL or nmol/L and needs a different factor
- Comparing values from two different immunoassays: the unit conversion is exact, but the methods are not interchangeable
- Interpreting thyroid status on its own; fT4 is read together with TSH and the clinical picture
How it is calculated
fT4 (pmol/L) = fT4 (ng/dL) × 12.87
Clinical pearls and limitations
- Converts units only; reference ranges depend on the laboratory, the assay and the patient.
- 1 ng/dL = 12.87 pmol/L; conversely, 1 pmol/L ≈ 0.078 ng/dL.
- Report pmol/L to one decimal place; more digits suggest a precision the immunoassay does not have.
- Reference intervals are method- and laboratory-specific; a converted value must be read against the interval of the lab that measured it.
- Free hormone immunoassays are susceptible to interference (e.g. biotin supplements, heterophile antibodies); an implausible fT4 is a reason to discuss the sample with the laboratory, not to recalculate.
- Do not mix up fT4 (ng/dL) with total T4 (µg/dL): the units differ by a factor of 1000 and the analytes are different.
Frequently asked questions
How do I convert free T4 from ng/dL to pmol/L?
Multiply by 12.87. Example: 1.2 ng/dL × 12.87 = 15.4 pmol/L; 2.5 ng/dL × 12.87 = 32.2 pmol/L.
What is 1 ng/dL fT4 in pmol/L?
12.87 pmol/L.
Why is the factor 12.87?
One mole of thyroxine weighs 776.87 g. Converting ng/dL to ng/L (× 10) and dividing by the molar mass gives nmol/L, which × 1000 is pmol/L: 10 000 ÷ 776.87 ≈ 12.87.
Can I compare fT4 from two different labs after converting?
Only roughly. The unit conversion removes the unit difference, but free-hormone assays from different manufacturers give systematically different results, so each value should be judged against its own lab's reference interval.
Evidence and guidelines
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<p><a href="https://medelix.ai/en/calculators/free-t4-ng-dl-to-pmol-l">Free T4 (fT4) ng/dL → pmol/L calculator by Medelix</a></p>For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.