Enter the Free T3 level and Reverse T3 level into the calculator to determine the Reverse T3 Ratio. This calculator can also evaluate any of the variables given the others are known.

Reverse T3 Ratio Formula

The following formula is used to calculate the Reverse T3 Ratio.

RTR = (FT3 / rT3) * 100


  • RTR is the Reverse T3 Ratio (%) FT3 is the Free T3 level (pg/mL) rT3 is the Reverse T3 level (ng/dL)

To calculate the Reverse T3 Ratio, divide the Free T3 level by the Reverse T3 level, then multiply the result by 100. This will give you the Reverse T3 Ratio in percentage.

What is a Reverse T3 Ratio?

A Reverse T3 Ratio is a measure used in the field of endocrinology to assess thyroid function. It involves comparing the levels of Reverse T3 (RT3), an inactive form of the thyroid hormone, to the levels of Free T3 (FT3), the active form of the hormone. A high RT3 ratio may indicate a condition known as Reverse T3 Dominance, where the body is producing too much RT3 and not enough FT3, leading to symptoms of hypothyroidism despite normal thyroid-stimulating hormone (TSH) levels.

How to Calculate Reverse T3 Ratio?

The following steps outline how to calculate the Reverse T3 Ratio:

  1. First, determine the Free T3 level (FT3) in pg/mL.
  2. Next, determine the Reverse T3 level (rT3) in ng/dL.
  3. Next, use the formula RTR = (FT3 / rT3) * 100 to calculate the Reverse T3 Ratio.
  4. Finally, calculate the Reverse T3 Ratio (%).
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Free T3 level (FT3) = 3.5 pg/mL

Reverse T3 level (rT3) = 0.8 ng/dL