Reverse T3 Ratio Calculator
The free T3 to reverse T3 ratio is one of the most important and overlooked markers of thyroid function. Most doctors rely on TSH alone, but your TSH can look completely normal while your cells are being actively blocked by reverse T3.
This calculator uses your free T3 and reverse T3 lab values to calculate your ratio and tells you whether or not you have optimal thyroid conversion, early stage pooling, or significant reverse T3 dominance. Enter your lab results below to get your results in seconds.
Reverse T3 Ratio Calculator
Enter your free T3 (pg/mL) and reverse T3 (ng/dL) values to calculate your ratio and see where your thyroid conversion stands.
Written and reviewed by Dr. Westin Childs, D.O.
How to Use This Calculator:
Step #1: Get Your Lab Results
You’ll need two specific values from your thyroid lab panel: your free T3 (in pg/mL) and your reverse T3 (in ng/dL). These are not included in the standard TSH-only lab panel, so you may need to specifically request them from your doctor or order them through a direct lab service.
If your results are in different units, here’s how to convert them:
- Free T3 in pmol/L -> pg/mL: Divide by 1.536 (example 5.0 pmol/L divided by 1.536 = 3.26 pg/mL)
- Free T3 in pg/dL -> pg/mL: Divide by 100 (example 320 pg/dL divided by 100 = 3.2 pg/mL)
- Reverse T3 in pg/mL -> ng/dL: Divide by 10 (example 150 pg/mL divided by 10 = 15 ng/dL)
- Reverse T3 in pmol/L -> ng/dL: Divide by 0.1536 (example 2.3 pmol/L divided by 0.1536 = 15 ng/dL)
Step #2: Enter Your Numbers
Type your free T3 value and your reverse T3 value into the fields above and click “Calculate My Ratio”.
The calculator automatically handles the unit conversion and calculates your ratio.
Step #3: Read Your Result
Your result will display instantly with your ratio score and one of three interpretations:
- Optimal (≥ 20)
- Suboptimal/Mild Pooling (10-19)
- Severe Thyroid Resistance (<10)
Each result includes an explanation of what it means for your symptoms and a recommended next step.
Understanding Your Results
Optimal Ratio (≥20): Normal Thyroid Conversion
A ratio of 20 or higher means your body is successfully converting T4 into active free T3 and is clearing reverse T3 efficiently.
At this level, you do not have significant thyroid pooling or cellular hypothyroidism.
If you are symptomatic despite having this optimal ratio, the issue is more likely related to:
- Overall thyroid hormone level (your free T3 is too low)
- Adrenal function or cortisol level
- Nutrient deficiencies
Suboptimal Ratio (10–19): Thyroid Pooling
A ratio between 10 and 19 indicates that your body is producing more reverse T3 than is optimal relative to your free T3 level.
Even if your TSH and free T4 are within the “normal” range, you may experience classic hypothyroid symptoms such as fatigue, weight gain, brain fog, and hair loss. At this ratio, your active thyroid hormone will have a difficult time reaching and activating your cells.
This is one of the most common patterns seen in patients who are on levothyroxine but still feel symptomatic.
A ratio at this level can often be remedied wth lifestyle changes.
Severe Thyroid Resistance (<10): Reverse T3 Dominance
A ratio below 10 is a strong indicator of reverse T3 dominance and cellular hypothyroidism.
At this level, your body is actively shunting T4 thyroid hormone down the reverse T3 pathway. This pattern is associated with more severe hypothyroid symptoms and is typically triggered by stress, inflammation, crash dieting, and leptin resistance.
A ratio at this level often requires both lifestyle and thyroid medication changes to remedy.
Frequently Asked Questions
The free T3 to reverse T3 ratio is calculated by dividing your free T3 (converted to pg/dL) by your reverse T3 (in ng/dL). To convert free T3 from pg/mL to pg/dL, multiply it by 100, then divide that number by your reverse T3 value.
For example, a free T3 of 3.2 pg/mL and a reverse T3 of 15 ng/dL gives a ratio of 21.3, which falls in the optimal range.
Use the calculator above to get your result instantly without the need to do the math manually (you’ll also get an instant interpretation to see if you are optimal).
The optimal free T3 to reverse T3 ratio is generally considered to be 20 or higher. A ratio between 10 and 20 is considered to be suboptimal and may indicate reverse T3 pooling, which indicates your body is converting too much T4 into the inactive reverse T3 metabolite rather than the active free T3 hormone.
A ratio below 10 is considered to be a sign of severe reverse T3 dominance, frequently associated with significant hypothyroid symptoms, even if the TSH is considered normal.
So summarize:
- A ratio < 10 = severe reverse T3 pooling
- A ratio between 10-19 = sub optimal T4 to T3 conversion
- A ratio > 20 = optimal reverse T3 ratio
These thresholds have been established by thyroid specialists based on their experience in monitoring the symptoms of patients with different ratios.
A reverse T3 is considered to be high when it exceeds 15-20 ng/dL. There are situations in which a high reverse T3 may be acceptable, though, which is why you need to look at it in relation to free T3 levels.
A reverse T3 of 20 ng/dL in someone with a free T3 of 4.0 pg/mL will still give you an optimal free t3:reverse t3 ratio, even though the reverse T3 is considered to be elevated.
This is why most functional medicine practitioners look at both free T3 and reverse T3 in relation to one another rather than as a standalone value.
The standard range for reverse T3 typically falls between 9-27 ng/dL, but falling within this range does not mean that your thyroid conversion is optimal.
Reverse ranges are designed to capture 95% of the population and do not define what is “healthy” or “optimal”, and a reverse T3 at the high end of that range (greater than 20 ng/dL) when the free T3 is not high enough has the potential to produce significant hypothyroid symptoms.
What matters more than your raw reverse T3 level is your free T3 to reverse T3 ratio, which tells you how well your thyroid hormone is being used by your cells and body.
Yes, and this is one of the most common and underdiagnosed thyroid lab patterns in thyroid patients.
TSH measures the signal sent from the brain to the thyroid gland, not the amount of thyroid hormone being produced from the gland or the amount being activated or used by the body at the cellular level.
A person can have a completely normal TSH while simultaneously having a poor free T3 to reverse T3 ratio, indicating their cells are being flooded with the thyroid-blocking metabolite reverse T3.
This condition is often referred to as cellular hypothyroidism or reverse T3 pooling, and it produces the classic signs of hypothyroidism, such as fatigue, weight gain, brain fog, and hair loss. This can occur even with completely “normal” thyroid lab test results.
Mild thyroid pooling is considered when a free T3 to reverse T3 ratio is below 20. Moderate to severe thyroid pooling is considered when a free T3 to reverse T3 ratio is less than 15.
Thyroid pooling occurs when the body preferentially converts T4 into the reverse T3 metabolite instead of the active free T3 thyroid hormone.
This process results in the blocking of active thyroid hormone (T3) from interacting with the thyroid nuclear receptor inside cells.
The lower the ratio, the more severe the pooling, and the more likely the person is to experience hypothyroid symptoms that will be missed by standard thyroid lab tests, such as the TSH and free T4.
You can check where your ratio falls using the free T3 to reverse T3 calculator on this page
A high reverse T3 is strongly associated with fatigue because it prevents free T3 from interacting with the thyroid nuclear receptor and the production of cellular energy in the form of ATP.
When reverse T3 blocks free T3 from doing its job, there is less thyroid hormone activation of the cells, which often leads to hypothyroid symptoms such as unexplained fatigue. This can occur even in thyroid patients with a normal TSH taking thyroid medications such as levothyroxine.
These thyroid patients often find the source of their fatigue when they check their free T3 to reverse T3 ratio.
The most common causes of elevated reverse T3 include stress, inflammation, calorie restriction, crash dieting, and leptin resistance.
These conditions all cause changes in the body that alter thyroid hormone conversion and signal to the body that energy must be preserved. This results in changes to thyroid physiology which encourage the production of reverse T3 from T4, instead of the production of free T3.
Other conditions that contribute to an elevated reverse T3 include iron deficiency, selenium deficiency, elevated cortisol, and some prescription medications like beta-blockers and amiodarone.
When attempting to lower reverse T3, it is essential that these root causes be addressed and resolved.
Yes. In fact, diet is one of the most significant modifiable factors affecting reverse T3 levels.
The primary factor influencing reverse T3 levels is calorie intake. Crash diets, very low-calorie diets, and prolonged fasting all cause spikes in reverse T3 levels within days to weeks because the body interprets these as a starvation signal in an attempt to conserve energy.
Some dietary changes can improve reverse T3 levels, including adequate protein intake, a whole food diet rich in minerals and vitamins, and adequate carbohydrate intake.
People with a history of chronic yo-yo dieting or calorie restriction often have chronically elevated reverse T3 levels, which are difficult to normalize.
Reverse T3 is controversial primarily because mainstream endocrinologists do not recognize it as an actionable lab test. This view is challenged by functional and integrative medicine practitioners who consider it essential for the proper evaluation and treatment of hypothyroid patients.
The conventional position is that reverse T3 is an inert breakdown product of T4 with no significant physiological effect. Emerging research suggests that reverse T3 has the potential to bind to thyroid receptors and competitively inhibit free T3 activity.
This debate hinges on the disagreement about whether standard thyroid lab tests (such as the TSH and free T4) are sufficient to adequately assess thyroid function or whether the more comprehensive thyroid lab panel (which includes free T3 and reverse T3) is required, especially in those thyroid patients who continue to experience low thyroid symptoms with “normal” lab tests.