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Free Thyroxine (FT4) Unit Converter
Free Thyroxine (FT4) represents the small fraction (approximately 0.03%) of circulating thyroxine that is unbound to proteins and biologically active. It is considered a more accurate indicator of thyroid status than Total T4, especially when binding proteins (like TBG) are abnormal.
Clinically, FT4 is measured alongside TSH to diagnose hypothyroidism and hyperthyroidism. Reporting units vary by region: the US typically uses mass units (ng/dL), while many other countries use the SI molar unit (pmol/L).
Mass Units (US)
StandardNanograms per deciliter (Common US Unit).
SI Units / Molar
Picomoles per liter (International Standard).
Clinical Context
Reference Ranges (Adults):
• Conventional: 0.9 – 1.7 ng/dL (approx).
• SI: 12 – 22 pmol/L.
Interpretation:
• High FT4: Hyperthyroidism, acute thyroiditis.
• Low FT4: Hypothyroidism, pituitary failure (central hypothyroidism).
Conversion Logic:
Molecular Weight of T4: ~776.87 g/mol.
1 ng/dL ≈ 12.87 pmol/L.
1 pmol/L ≈ 0.0777 ng/dL.
Clinical References
How to Use This Converter
Follow these steps to normalize FT4 values.
Enter Values
Input your laboratory result into the corresponding unit field (e.g., ng/dL).
Automatic Conversion
The calculator converts between mass units and the SI molar unit using the molecular weight of 776.87 g/mol.
Reset
Use the Clear button to reset all fields.
Frequently Asked Questions
No. 1 nanogram per deciliter (ng/dL) equals 10 picograms per milliliter (pg/mL).
Total T4 is affected by binding proteins like TBG. Pregnancy or birth control pills increase TBG, raising Total T4, while FT4 often remains normal.