What Is the Normal Size of a Thyroid Gland?

As is true for all nature, much anatomical variation exists in people. Many factors can influence the size of individuals, their glands and organs. Size variation in the thyroid gland is no exception, and is influenced by such factors as genetics, maternal diet and fetal development.


The thyroid gland is a horseshoe-shaped, ductless endocrine gland that lies in front of the upper portion of the trachea. It secretes thyroid hormone and calcitonin.

Normal Size Range

According to endocrinologist Dr. Mark Lupo, normal dimensions for the thyroid gland are 4 to 4.8 x 1.0 to 1.8 x 0.8 to1.6 cm. However, dimensions that fall outside of this range do not necessarily signify abnormal pathology.

Factors Affecting Size

People who live and grew up in countries where iodine is prevalent in the diet, such as the United States, Britain, Japan and Iceland, will in general have thyroids that are smaller. During pregnancy, women often experience a temporarily larger thyroid. And in general, the thyroids of smokers are larger than average.


While manual palpitation may be responsible for initial identification of a potentially enlarged thyroid, a thyroid scan is a more accurate way to visualize its size and shape. Because the thyroid gland is a soft tissue, it will not show up on an X-ray. The usual method for viewing the gland is by thyroid ultrasound--a painless, non-invasive procedure performed at a radiology lab.


An enlarged thyroid gland is referred to as a goiter. Goiters are often endemic in populations where soil, hence diets, are low in iodine.