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Free T4 (fT4) pmol/L → ng/dL

Convert free t4 (ft4) from pmol/L to ng/dL

Sources last checked: 2026-11-03

Free T4 (fT4) pmol/L → ng/dL

Convert free t4 (ft4) from pmol/L to ng/dL

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Converts units only; reference ranges depend on the laboratory, the assay and the patient.

Source: AMA Manual of Style, 11th ed. (Oxford Academic) — Units of measure converter, Table 2: Selected laboratory tests and conversion factors.Open

What is the Free T4 (fT4) pmol/L → ng/dL?

This converter turns free thyroxine (fT4) reported in pmol/L — the SI unit used in the UK, Scandinavia and most European guidelines — into ng/dL, the conventional unit used in the USA, Turkey and many German-speaking laboratories. It divides by 12.87, the AMA Manual of Style factor derived from the molar mass of thyroxine (776.87 g/mol).

When to use it

  • Reading a European discharge letter or report in pmol/L when the local lab reports ng/dL
  • Comparing a new result with older values documented in ng/dL
  • Working through US textbooks, question banks or studies that use conventional units

When not to use it

  • Total T4 in nmol/L — that is a different analyte with a different factor
  • Transferring a reference interval from one assay to another; intervals do not convert reliably between methods

How it is calculated

fT4 (ng/dL) = fT4 (pmol/L) ÷ 12.87

Clinical pearls and limitations

  • Converts units only; reference ranges depend on the laboratory, the assay and the patient.
  • 1 pmol/L ≈ 0.078 ng/dL; 10 pmol/L ≈ 0.78 ng/dL.
  • Two decimal places in ng/dL are enough; results are usually printed that way.
  • Some laboratories report fT4 in ng/L (not ng/dL); 1 ng/dL = 10 ng/L, so check the denominator before converting.
  • If fT4 and TSH do not fit together, assay interference or a non-thyroidal illness is more likely than a unit error — but a unit error is the first thing to exclude.

Frequently asked questions

How do I convert free T4 from pmol/L to ng/dL?

Divide by 12.87. Example: 16 pmol/L ÷ 12.87 = 1.24 ng/dL; 20 pmol/L ÷ 12.87 = 1.55 ng/dL.

What is 1 pmol/L fT4 in ng/dL?

About 0.078 ng/dL (1 ÷ 12.87).

Is fT4 in pmol/L the same as T4 in nmol/L?

No. pmol/L values are free thyroxine; nmol/L values are usually total T4, which includes protein-bound hormone and is a different measurement.

Evidence and guidelines

  1. Primary source: AMA Manual of Style, 11th ed. (Oxford Academic) — Units of measure converter, Table 2: Selected laboratory tests and conversion factors.
  2. PubChem compound summary: thyroxine (CID 5819), molecular weight 776.87 g/mol.

Have a follow-up question?

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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.