Free T3: normal range and what it means
Short answer: The normal Free T3 range is 2.3 – 4.2 pg/mL for adults. In SI units that is about 3.5 – 6.5 pmol/L. Labs differ a little, so also check the range printed on your report.
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Where does your Free T3 sit?
Same number as ng/L.
Your result
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Information, not a diagnosis. Talk to a doctor about your result, and sooner if you feel unwell.
The active thyroid hormone driving metabolism.
Normal range
Adult reference range.
- Low< 2.3 pg/mL
- Normal2.3 – 4.2 pg/mL
- High≥ 4.2 pg/mL
What it measures
The unbound, more active thyroid hormone, most of it converted from T4 in the tissues. It falls in illness and in prolonged energy restriction even when the thyroid is fine.
What moves it
Conversion from T4, which slows during illness, calorie restriction and prolonged stress. Often the first thyroid number to dip when the body is under strain.
How to bring it into range
Selenium and adequate calories support conversion. Aggressive dieting lowers it, which is expected rather than a thyroid problem.
How fast it responds
Four to six weeks.
Also reported as: ft3 · free triiodothyronine
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Common questions
- What is the normal Free T3 range?
- The normal Free T3 range is 2.3 – 4.2 pg/mL for adults. In SI units that is about 3.5 – 6.5 pmol/L. Labs differ a little, so also check the range printed on your report.
- What does a high Free T3 mean?
- A value above the reference band means Free T3 is outside the range typical for a healthy adult. A single reading is rarely conclusive on its own — what matters is the trend across draws and the other markers around it, which is why HealthOS reads the whole panel together rather than one number at a time.
- How do I improve my Free T3?
- Selenium and adequate calories support conversion. Aggressive dieting lowers it, which is expected rather than a thyroid problem.
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Reference ranges are general-population guidance compiled from common clinical laboratories, not a diagnosis. Lab-to-lab ranges differ. Always read your results with your doctor.