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Free T3 (fT3) pg/mL → pmol/L

Convert free t3 (ft3) from pg/mL to pmol/L

Sources last checked: 2026-11-03

Free T3 (fT3) pg/mL → pmol/L

Convert free t3 (ft3) from pg/mL to pmol/L

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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 T3 (fT3) pg/mL → pmol/L?

Free triiodothyronine (fT3) is reported in pg/mL in the USA, Turkey and many German and Austrian laboratories, and in pmol/L in SI-based systems such as the UK and Scandinavia. This converter multiplies by 1.536, derived from the molar mass of liothyronine (650.97 g/mol) as used in the AMA Manual of Style SI table.

When to use it

  • Reading guidelines or papers that quote fT3 in pmol/L
  • Comparing a pg/mL result with an earlier value from an SI-reporting lab
  • Preparing reports or exam answers in SI units

When not to use it

  • Total T3, often reported in ng/dL or nmol/L, which needs a different factor
  • Comparing results from different immunoassays as if they were interchangeable

How it is calculated

fT3 (pmol/L) = fT3 (pg/mL) × 1.536

Clinical pearls and limitations

  • Converts units only; reference ranges depend on the laboratory, the assay and the patient.
  • 1 pg/mL = 1.536 pmol/L; 1 pmol/L ≈ 0.651 pg/mL.
  • Free T3 is a small fraction of total T3; the free and total assays answer different questions.
  • fT3 assays are method-dependent; reference intervals belong to the laboratory that measured the sample.
  • Watch for pg/dL or ng/L on unusual reports — check the denominator before applying 1.536.

Frequently asked questions

How do I convert fT3 from pg/mL to pmol/L?

Multiply by 1.536. Example: 3.0 pg/mL × 1.536 = 4.6 pmol/L; 4.2 pg/mL × 1.536 = 6.5 pmol/L.

What is 1 pg/mL free T3 in pmol/L?

1.536 pmol/L.

Where does the factor 1.536 come from?

pg/mL equals ng/L. Dividing by the molar mass of T3 (650.97 g/mol) gives nmol/L, and × 1000 gives pmol/L: 1000 ÷ 650.97 ≈ 1.536.

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: liothyronine (triiodothyronine) (CID 5920), molecular weight 650.97 g/mol.

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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.