Free T3 Percentage & Unit Converter
Calculate your thyroid hormone position within the laboratory reference range.
Understanding Your Free T3 Levels
Free Triiodothyronine (FT3) is the active form of the thyroid hormone T3. While total T3 measures both bound and unbound hormones, Free T3 measures only the hormone that is available to enter your cells and regulate metabolism. Monitoring this value is critical for patients with hypothyroidism, hyperthyroidism, or Hashimoto's thyroiditis.
Why Calculate the Percentage in Range?
Lab reference ranges are often very broad. A result can be "within range" but still suboptimal for your specific health needs. Functional medicine practitioners often suggest that "optimal" thyroid function typically resides in the upper 25% to 50% of the lab's reference range. This calculator helps you pinpoint exactly where your levels fall.
Conversion Math: pg/mL to pmol/L
Different laboratories use different units depending on their location. In the United States, pg/mL (picograms per milliliter) is standard, while the UK, Canada, and Australia typically use pmol/L (picomoles per liter). To convert between them, we use the following constants:
- pg/mL to pmol/L: Multiply by 1.536
- pmol/L to pg/mL: Divide by 1.536
Typical Reference Ranges
While ranges vary by lab, a common adult reference range for Free T3 is approximately 2.3–4.2 pg/mL (3.5–6.5 pmol/L). If your percentage is 0%, you are at the bottom of the range. If it is 100%, you are at the top. Results above 100% or below 0% indicate your levels are outside the lab's established normal boundaries.
Practical Example
If your FT3 is 3.1 pg/mL and your lab's range is 2.3 to 4.2 pg/mL:
1. (3.1 – 2.3) = 0.8
2. (4.2 – 2.3) = 1.9
3. (0.8 / 1.9) * 100 = 42.1%
In this case, you are sitting at roughly the 42nd percentile of the range.