Thyroid Lab Unit Converter: pmol/L, ng/dL, pg/mL Made Simple
Your lab report and the ranges online don't use the same units. Convert any thyroid lab in one step:
Written and medically reviewed by Dr. Westin Childs, D.O. Last reviewed: August 28, 2026
Why Your Labs And The Internet Never Match
You look up an optimal free T4 range and find 1.4 to 1.77. Your lab report says 17.2. Nothing is wrong with either number: US labs report in ng/dL and pg/mL, most of the rest of the world reports in pmol/L and nmol/L, and nobody warns you.
The converter above handles every thyroid lab: TSH, free T4, free T3, total T4, total T3, reverse T3, thyroglobulin, and both antibodies, with the optimal range shown in both unit systems so you always know where you stand.
A few of them, like TSH and the antibodies, are the same number in both systems. The converter tells you when that’s the case, so you can stop second-guessing.
Frequently Asked Questions
Divide by 12.87. A free T4 of 18 pmol/L is 1.4 ng/dL. Going the other way, multiply: 1.4 ng/dL times 12.87 gives 18 pmol/L. The converter above does this for you and shows the optimal range in both units.
Divide by 1.536. A free T3 of 5.8 pmol/L is about 3.8 pg/mL, which happens to be the bottom of the optimal range. Multiply by 1.536 to go from pg/mL back to pmol/L.
Because mIU/L and uIU/mL are the same concentration written two ways. A TSH of 2.5 is 2.5 in both systems. The same is true for thyroglobulin (ng/mL equals ug/L) and for both thyroid antibodies (IU/mL equals kIU/L).
Some US labs report reverse T3 in ng/dL and some in pg/mL, and the difference is a factor of 10: 15 ng/dL equals 150 pg/mL. Check the unit printed on your report before comparing to any range, because this exact mixup makes normal results look alarming.
Related Tools
- Optimal Thyroid Lab Calculator: see where your converted numbers fall
- T4 to T3 Conversion Calculator: score how well you convert
- All Thyroid Calculators & Quizzes: the full set of free tools
Scientific References
- Kratzsch J, Baumann NA, Ceriotti F, et al. Global FT4 immunoassay standardization: an expert opinion review. Clin Chem Lab Med. 2021;59(6):1013-1023.
- Thienpont LM, Van Uytfanghe K, De Grande LAC, et al. Harmonization of serum thyroid-stimulating hormone measurements paves the way for the adoption of a more uniform reference interval. Clin Chem. 2017;63(7):1248-1260.