fT3 / fT4 Value Calculator | Convert Thyroid Values into Percent

Many labs use very different norm values ​​and reference ranges to represent blood values in numbers. This poses a problem when the patient wants to compare his blood levels from different laboratories.

But also the ratio of fT3 to fT4 is important for a good well-being and can only be represented in relative percent. If the free thyroid levels are in the lower third, you can assume that there is a hypofunction of the thyroid gland and a hormone dose increase would be useful.

On the other hand, most Hashimoto patients feel comfortable with free thyroid levels above 50%. In my case, I need fT3 values ​​between 80-100%. The ft4 is due to my intake of porcine hormones usually much lower, between 30-50%.

A small example for conversion into percent

In the following example, you can see very well how treacherous the estimation of absolute thyroid values ​​can be and how quickly the result is compared in percent. In January 2013, my free thyroid values were as follows:

fT3 (2.3 – 4.2) — 2.8 pg / ml
fT4 (0.8 – 1.8) — 1.1 ng / dl

At first glance, the blood levels look pretty good. Also the doctor told me that the values ​​were perfectly fine. If these laboratory values ​​are converted into percent, it quickly shows:

fT3 (2.3 – 4.2) — 2.8 pg / ml — 26.32%
fT4 (0.8 – 1.8) — 1.1 ng / dl — 30.00%

The values, calculated into percentage, ​​clearly indicate a hypofunction, which was immediately confirmed by an increase of the thyroid hormones. For this reason, I can only recommend each thyroid patient to convert his thyroid levels in percent and to compare permanently.

It is also useful to always make some notes on the respective hormone dose, including blood values. With the help of such records, a proper thyroid adjustment can be done relatively quick.

fT3 / fT4 – Value Calculator

Interpretation of the relative thyroid values in percent

  • Lower third: Presumably a hypofunction of the thyroid gland is present
  • Medium range (from 50%): Normal range with a smooth transition to the “feel-good area”
  • Upper third: For many Hashimoto patients, here begins the so-called “feel-good area”

Image source:

  • ft3-ft4-calculator: © Ghazi-Michael Ayed