Thyroid lab unit converter
Labs outside the US often report free T4, free T3 and reverse T3 in pmol/L. Convert them to US units (or back) before comparing with a range.
1 ng/dL = 12.87 pmol/L. TSH (mIU/L and µIU/mL) and antibodies (IU/mL and kIU/L) read the same in both units.
| Test | US unit | SI unit | US to SI |
|---|---|---|---|
| TSH | mIU/L | µIU/mL | × 1 |
| Free T4 | ng/dL | pmol/L | × 12.87 |
| Free T3 | pg/mL | pmol/L | × 1.536 |
| Reverse T3 | ng/dL | pmol/L | × 15.36 |
| TPO antibodies | IU/mL | kIU/L | × 1 |
| Thyroglobulin antibodies | IU/mL | kIU/L | × 1 |
Medically reviewed by Andrew Cunningham, MD, November 12, 2026.
Frequently Asked Questions
How do I convert free T4 from ng/dL to pmol/L?
Multiply by 12.87. For example, 1.2 ng/dL is about 15.4 pmol/L.
How do I convert free T3 from pg/mL to pmol/L?
Multiply by 1.536. For example, 3.2 pg/mL is about 4.9 pmol/L.
How do I convert reverse T3 from ng/dL to pmol/L?
Multiply by 15.36. For example, 15 ng/dL is about 230 pmol/L.
Is TSH the same in mIU/L and µIU/mL?
Yes. They are the same value written two ways, so no conversion is needed. Thyroid antibodies in IU/mL and kIU/L are also the same value.
Can I compare results from labs that use different units?
Convert them to the same unit first, then compare each with the range printed on its own report. Different labs also use different methods, so small differences between labs are normal.
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