Change of the thyroid gland volume is often the symptom of most common pathological conditions some thyroid diseases. The exact calculation for the thyroid volume is very important for the assessment and management of thyroid disorders. The volume of thyroid gland, using computed tomography (CT), ultrasound (USG) and magnetic resonance imaging (MRI) has been accessed in few studies published; however a gold standard method has not yet been determined. The purpose of this study was to estimate the volume of normal thyroid gland to define an optimal correction factor therefore was to compare different techniques using the CT. We used computed tomography images obtained from 8 cadavers (2 females, 6 males) to calculate the thyroid volumes. In the present study, the actual thyroid volumes were measured using the water-displacement method as a gold standard, point-counting as a stereology, and ellipsoid methods. Mean squared errors and correction factors were calculated and modeled for each model to find an optimal correction factor and from 0.450 to 0.600 in steps of 0.001 separately for thyroid volume estimation. The average volume of the thyroid glands were 14.58 +/- 9.84, 15.28 +/- 9.38, and 14.97 +/- 8.35 cm(3) by fluid displacement, stereology and ellipsoid formula, respectively. No significant difference was found among the methods (P>0.05). The results of this study suggested that the volume of thyroid gland can be measured on CT scans stereologically for diagnosis, as will as provide reliable measure of thyroid volume, management and follow-up of thyroid diseases and for preoperative planning.