How to Use the Free T4 Unit Conversion Calculator
Choose the conversion direction, enter the Free T4 value from your lab report, and read the result instantly. The calculator supports both pmol/L to ng/dL and ng/dL to pmol/L.
This page is focused on Free T4, also called free thyroxine. It is not the same as Total T4, which measures both bound and unbound hormone.
Free T4 Conversion Formula
Free T4 is commonly reported in pmol/L in many international lab reports and in ng/dL in many US-style thyroid panels. The common conversion factor is 12.87.
Free T4 ng/dL = Free T4 pmol/L ÷ 12.87 Free T4 pmol/L = Free T4 ng/dL × 12.87 The same relationship can also be written with the molecular weight of thyroxine: ng/dL = pmol/L × 776.87 ÷ 10000.
Example Free T4 Conversion
If your Free T4 result is 15 pmol/L, divide by 12.87:
15 ÷ 12.87 = 1.17 ng/dL For the reverse direction, multiply by 12.87. A Free T4 value of 1.2 ng/dL is about 15.4 pmol/L.
Free T4 pmol/L to ng/dL Chart
Use this chart to compare common Free T4 values between pmol/L and ng/dL. Reference ranges vary by lab and assay.
| Free T4 pmol/L | Free T4 ng/dL | Note |
|---|---|---|
| 8 pmol/L | 0.62 ng/dL | Often below typical adult range |
| 10 pmol/L | 0.78 ng/dL | Low-normal area in many labs |
| 12 pmol/L | 0.93 ng/dL | Common normal value |
| 15 pmol/L | 1.17 ng/dL | Common normal value |
| 18 pmol/L | 1.40 ng/dL | Common normal value |
| 20 pmol/L | 1.55 ng/dL | High-normal area in many labs |
| 22 pmol/L | 1.71 ng/dL | Often above typical adult range |
| 25 pmol/L | 1.94 ng/dL | Elevated in many lab ranges |
| 30 pmol/L | 2.33 ng/dL | Clearly elevated in many adult reports |
ng/dL to pmol/L Reverse Chart
If your thyroid report uses ng/dL and you want the SI-style pmol/L value, use this reverse chart.
| Free T4 ng/dL | Free T4 pmol/L |
|---|---|
| 0.7 ng/dL | 9.0 pmol/L |
| 0.8 ng/dL | 10.3 pmol/L |
| 1.0 ng/dL | 12.9 pmol/L |
| 1.2 ng/dL | 15.4 pmol/L |
| 1.4 ng/dL | 18.0 pmol/L |
| 1.6 ng/dL | 20.6 pmol/L |
| 1.8 ng/dL | 23.2 pmol/L |
| 2.0 ng/dL | 25.7 pmol/L |
| 2.5 ng/dL | 32.2 pmol/L |
Free T4 vs TSH and Free T3
Free T4 is one part of a thyroid panel. TSH often reflects how strongly the pituitary gland is signaling the thyroid, while Free T3 reflects the active thyroid hormone available in circulation. Free T4 is commonly reviewed with both values.
A unit conversion helps compare reports, but it does not explain the pattern by itself. The same Free T4 value can mean different things depending on TSH, Free T3, symptoms, medications, and pregnancy status.
Common Mistakes to Avoid
Do not use the Free T3 conversion factor for Free T4. T3 and T4 have different molecular weights, so their unit conversions are different.
Do not mix Free T4 and Total T4 reference ranges. Free T4 is usually reported in pmol/L or ng/dL, while Total T4 may use units such as µg/dL or nmol/L.
Always compare your converted value with the reference range from the same lab report when possible. Thyroid assays can vary between laboratories.
Frequently Asked Questions
How do you convert Free T4 pmol/L to ng/dL?
Divide the Free T4 value in pmol/L by 12.87. For example, 15 pmol/L is about 1.17 ng/dL.
How do you convert Free T4 ng/dL to pmol/L?
Multiply the ng/dL value by 12.87. For example, 1.2 ng/dL is about 15.4 pmol/L.
What is 1.0 ng/dL Free T4 in pmol/L?
1.0 ng/dL Free T4 equals about 12.87 pmol/L.
What is 20 pmol/L Free T4 in ng/dL?
20 pmol/L divided by 12.87 equals about 1.55 ng/dL.
Is Free T4 the same as Total T4?
No. Free T4 measures unbound thyroxine, while Total T4 includes hormone bound to proteins plus the free fraction.
Can this calculator diagnose thyroid disease?
No. This tool only converts units. Thyroid interpretation requires clinical context and usually includes TSH, Free T4, sometimes Free T3, medication history, and symptoms.
Conclusion
This Free T4 unit conversion calculator helps you compare thyroid lab results across pmol/L and ng/dL reporting systems. Use it for accurate unit conversion, then rely on your healthcare provider to interpret the result in the context of your full thyroid panel.