“A normal adult thyroid gland weighs 10 to 20 g and the thyroid secretes two hormones. Thyroxine (T₄) makes about 90% of hormone production, and triiodothyronine (T₃) produces the other 10%. Peripheral tissues convert T₄ to T₃, and most of T₃ is derived from T₄.”

Cleveland Clinic (center for continuing education)