1.2 ng/dL free thyroxine (FT4) to pmol/L

About free thyroxine (FT4) and these units

Free thyroxine (FT4) is the unbound fraction of the thyroid hormone thyroxine, reported on thyroid panels. Free thyroxine appears in ng/dL on US lab reports and in pmol/L on UK, Canadian, Australian, and most European lab reports. The factor (12.87) reflects reporting in picomoles per liter, a millionfold smaller molar unit than millimoles per liter.

Where the 12.87 conversion factor comes from

ng/dL is a mass-per-volume unit. pmol/L is a moles-per-volume (molar concentration) unit. To convert between them you need the molecular weight of the substance, because that determines how many moles of it fit into a given mass.

For free thyroxine (FT4), the reference molecular weight is 776.87 g/mol. Working through the unit algebra:

• The factor is fixed by the molecular weight (776.87 g/mol) together with the mass and volume prefixes of the two units, since a molar concentration counts molecules and a mass concentration weighs them.
• For free thyroxine (FT4) this works out to 12.87 pmol/L per ng/dL (multiply ng/dL by 12.87 to get pmol/L).
• The inverse (pmol/L → ng/dL) is 0.0777.

Step-by-step: converting 1.2 ng/dL of free thyroxine (FT4) by hand

1. Start with the lab value: 1.2 ng/dL.
2. Look up the conversion factor for free thyroxine (FT4): 12.87 pmol/L per ng/dL.
3. Multiply: 1.2 × 12.87 = 15.444.
4. Attach the SI unit: 15.444 pmol/L.

Inverse check: 15.444 pmol/L ÷ 12.87 = 1.2 ng/dL ✓.

Companion conversions for nearby free thyroxine (FT4) values

If your lab reported a number close to but not exactly 1.2 ng/dL, the table below covers the surrounding range so you don't need to re-run the arithmetic.

A note on precision

Clinical chemistry assays for free thyroxine (FT4) are typically precise to two or three significant figures. The exact factor 12.87 is itself a rounded number, and the molecular weight that produces it (776.87 g/mol) is conventionally rounded. So while the calculator displays 15.444 pmol/L for 1.2 ng/dL, reporting more decimal places than your original measurement supports is false precision.

Common questions

What is 1.2 ng/dL free thyroxine (FT4) in pmol/L?

1.2 ng/dL of free thyroxine (FT4) equals 15.444 pmol/L. The conversion factor for free thyroxine (FT4) is 12.87 (multiply ng/dL by 12.87 to get pmol/L).

How do I convert ng/dL to pmol/L for free thyroxine (FT4)?

free thyroxine (FT4) has a conversion factor of 12.87. Formula: 1.2 ng/dL × 12.87 = 15.444 pmol/L. Inverse: 15.444 pmol/L ÷ 12.87 = 1.2 ng/dL.

Why does free thyroxine (FT4) have a different conversion factor than other biomarkers?

Each biomarker's ng/dL ↔ pmol/L factor is set by its molecular weight, because pmol/L is a molar concentration. For free thyroxine (FT4), the reference molecular weight is 776.87 g/mol, which gives a factor of 12.87.

Where is ng/dL used and where is pmol/L used?

Free thyroxine appears in ng/dL on US lab reports and in pmol/L on UK, Canadian, Australian, and most European lab reports. The factor (12.87) reflects reporting in picomoles per liter, a millionfold smaller molar unit than millimoles per liter.

How precise should I report the converted value?

Lab assays for free thyroxine (FT4) are typically precise to about two or three significant figures. Reporting more decimal places than your original measurement supports is false precision. For a reading of 1.2 ng/dL, 15.444 pmol/L is appropriate; further decimals are not.

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