Expert Guidance From Louise O’Connor - The Thyroid Naturopath { Discover More! }

Learn How to Calculate Your Reverse T3 Ratio

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reverse T3 ratioThere’s a simple way to calculate your reverse T3 ratio. But before you can do this you need your lab results for free T3, and reverse T3 (RT3).

What Does The Reverse T3 Test Measure?

The reverse T3 test measures how much reverse T3 is circulating in the bloodstream.

The result takes on far greater meaning when the total amount of reverse T3 is compared to the total amount of ‘free T3’. This post explains how to calculate the reverse T3 ratio.

How to Calculate Your Reverse T3 Ratio

To work out your reverse T3/T3 ratio divide the total free T3 by the total reverse T3 and multiply this by 100.

The standard reference range for the FT3: Reverse T3 ratio is currently 1.200 – 2.200.

If your reverse T3/T3 ratio is at the lower end, or below this range it indicates you have a thyroid hormone imbalance.

Your thyroid blood results can be a little confusing. So here is a real example to help explain how you can calculate your own reverse T3/T3 ratio.

Example; free T3 is 4.3 pmol/L and reverse T3 is 704 pmol/L.

To work out the reverse T3 ratio divide 4.3 by 704 then multiply this by 100. The result is 0.610 which is well below the healthy range, and indicates this individual is dealing with reverse T3 dominance.

When Standard Thyroid Medication Isn’t Working

If you are worried your hypothyroid symptoms are due to excess RT3 it’s vital to seek out a thyroid-literate doctor who will take your concerns seriously.

A prescription for single T3 hormone replacement may be required.  This is often the most effective way to counter excess reverse T3. Keep in mind T3 thyroid medication can take a little while to work as it takes time to flush excess reverse T3 from the body.

What about T4 medication?

Levothyroxine is the standard of care for hypothyroidism but care needs to be taken with single T4 medication, or even a combination of T4/T3.

The reason is fairly straightforward – when you take supplemental T4 you essentially provide the body with more T4. This then has the potential to create more reverse T3, thereby perpetuating the problem.

What causes reverse T3?

If you’ve been diagnosed with high reverse T3 you may be wondering WHY. I answer this important question here on this blog post: What Causes High Reverse T3 (RT3)? {There Are 5 Key Reasons}

reverse T3 ratio

Has this blog helped you calculate your reverse T3 ratio? Did this give you new insights into your thyroid health? If so, it would be great if you could take a few moments to share with me in the comments below. You can also share this blog post with the world. Simply click on one of the social media icons on the left of your screen. Thank you for helping raise thyroid health awareness.


  1. Alice Grace Alanyo says:

    Thank you very much for the technical information. I really need it as I am undergoing such a problem.
    Thank you once more.

  2. Thank you for this calculation. Most sites point to “over 20” which if we go from these figures, would be over 2.0.

    Which range is correct?

    • Louise O'Connor says:

      A result over 20 for a reverse T3 to free T3 ratio may seem high. Are these sites using the same method to calculate the ratio? That is, divide the total free T3 by the total reverse T3 and multiply this by 100. It is also important to take into account the unit of measurement including the type of T3 – is it standard T3 or free T3? T3 and reverse T3 are usually reported using nmol/L or pmol/L.

  3. Jenny Bodenham says:

    My FT3 is 3.99 pmol/L and my rT3 is 0.38pmol/ml – could you clarify how I would work out the ratio please? Many thanks.

  4. Louise O'Connor says:

    The reverse T3 ratio is useful for individuals with high levels of reverse T3. Can I confirm your rT3 is written as 0.38pmol per millilitres not litres? If this correct your reverse T3 is equivalent to 380 pmol/L. (1000 millilitres = 1 litre). Using 380pmol/L as your reverse T3 total your ratio is 1.05. This calculation is done by dividing 3.99 by 380 X 100.

  5. I have a question. I recently visited a alternative medicine MD who tested my thyroid. He did not test my free T3, however, for what reason I don’t know. When he was calculating my ratio, he was mumbling something under his breath about the fact that he didn’t test my T3, but he would “calculate anyway. ” He calculated my ratio based on my T3 and my rT3 with a resulting ratio of 6.93. He said the ratio should be 10:1. , and recommended glandular support. Everything I am reading online says you must use the fT3. Also am finding that a ratio of less than 20 is indicative of a problem. Should I be concerned ??

    • Louise O'Connor says:

      It is possible to check your T3/reverse T3 ratio using the standard T3 result. Although testing free T3 is ideal. When you use T3 a ratio greater than 10 is considered best. When looking at your thyroid blood tests it is very important to look at all the test results and how they relate to each other. And also how they relate back to how you actually feel. In Australia the standard reference range for reverse T3 is 170 – 450pmol/L. Usually rT3 is reported in the hundreds so 16 seems low but maybe you are in a country with a different reporting system?

  6. I should have mentioned this in my previous post. My total T3 was 111 and my rT3 was 16.

  7. Sue Ivan says:

    Good Day,
    I am having a hard time converting my ratios. They are in US values.
    I have a Total T3 of 0.5 ng/ml and a RT3 of 13.9 ng/dL.

    I also have an elevated serum and urinary cortisol.

    Could you please provide some clarification.

    Thank you,

  8. Thank you so much for your helpful article. I did the calculation and my number was 5.70 and 7.33 for my son. This puts us very high. What does that mean for us? Your article only talks about being low. Thank you.

    • Louise O'Connor says:

      Vickie, is it possible to speak to your healthcare practitioner regarding your FT3 and RT3 results? In particular, ask to check if FT3 is possibly pooling in the body as this is a sign of an over active thyroid. Best wishes, Louise O’Connor

  9. My Free T3 is 2.92 pg/nL
    RT3 is 18.1 ng/mL
    Can you give me my ratio and tell me if it is high or low, please.

    • Louise O'Connor says:

      Lee Ann, first let’s convert your results to pmol/L. Therefore, using 2.92 pg/ml equivalent to 4.48 pmol/L, and 18.1ng/ml equivalent RT3 278 pmol/L the ratio is 0.016. If the numbers I am using are accurate this is not cause for concern. The RT3 at 278 would not normally be considered elevated. If you are continuing to experience hypothyroid symptoms I recommend looking at other markers such as thyroid antibodies. Best wishes, Louise O’Connor

  10. Hi Louise
    My ft3 is 4.5 and my rt3 is 785. Am I right thinking my ration is .05????
    I have just started T3 on top of my t4 Meds. I was great for the first ten days and then lost traction again. I have added zinc, magnesium, iron, methylated B and chaste tree to increase progesterone. How do I know if I should be removing t4 and on T3 only

    • Louise O'Connor says:

      Hi Tina, yes you have a very low ratio as your RT3 is high and FT3 could be considered low end of normal. Most functional medicine practitioners prescribe single T3 when a person has excess RT3. They don’t usually prescribe T4 medication. The reason is, the body can produce more RT3 from the supplemented T4. It would be best to discuss medication options with your Dr so together you can decide what is best for you. I also suggest you look at the reasons why your body is producing excess RT3. This post explains more: Best wishes, Louise O’Connor

  11. Hello
    My T3 is 3.7pmo/L and my RT3 is 767pmo/L . (I’m in Australia) I can not figure out the reason as I have a low fasting insulin, I’m not overweight, don’t feel particularly stressed – I do have PCOS but as I said low insulin. Irregular periods and trying to get pregnant. I’m at a loss as to what to do!

    • Louise O'Connor says:

      Hello Helen, as you may know thyroid problems are complex. It’s possible to have low T3 and high RT3 for a number of reasons. It’s therefore wise to work with a practitioner who can investigate the root causes, and then from there plan an effective treatment strategy. From my experience as a Naturopath it’s possible to improve free T3 and RT3 results once you address the root causes. Best wishes, Louise O’Connor.

  12. Susan Wasteney says:

    Hi Louise, nice to be back
    I recently had my rt3 tested via i-screen and it came in at 583 pmol/l, I showed my GP the results and she couldn’t
    be less interested….I’m Extremely cheesed off so have decided to go Dr shopping.
    I have been trialing 200mcg Eutrosig one day and 150mcg the next day which did Not make me feel any better so will ditch that and go back to 150mcg daily, My problem by the way is Atrophic Thyroiditis,
    My lovely Doc wants me to go to a Neurologist….What!!!!!
    My last two Tsh, FT3 and FT4 were; Tsh 0.17, Ft4 16.1 , Ft3 3.7 { April} pmol/l
    Tsh 0.07 , Ft4 15.9, Ft3 4.1 {May} pmol/l.
    What do you suggest I can do? feeling like road kill every day with constant tightness in my head all the time is
    not pleasant and very distracting.
    My eyes, sinuses and brain have all been scanned….at least I have a brain thank goodness.

    • Louise O'Connor says:

      Hi Susan it’s vital to discuss your concerns with a thyroid-literate doctor who understands how to safely and effectively use single T3 medication to bring down excess RT3. For those with RT3 well above normal they find they don’t tolerate single T4 medication. And this makes sense once you understand basic thyroid physiology. Single T4 can be problematic as it provides the body with greater amounts of T4 which is then easily converted through to RT3. Also suggest you check information on the circadian T3 method (CT3M) by Paul Robinson at the Recovering With T3 website.

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