Objectives: The present study was conducted to compare the accuracy of formulas used to calculate fetal thigh volume (FTV) using the virtual organ computer-aided analysis (VOCAL) technique with two-dimensional (2D) in formulas predicting birth weight. Materials and Methods: This was a prospective, cross-sectional study of 84 pregnant women with 72 hours of delivery evaluated at a university hospital between May, 2008 and April, 2010. After 2D ultrasounds (US) measurement, 3DUS was also used to determine FTV with estimates computed using the VOCAL program. Results: The correlation between fetal weight predicted by the 3D equation of FTV and the actual birth weight was significant. While FTV and the Hadlock II equation exhibited a low sensitivity for detection of low-birthweight infants, FTV was a more sensitive method of detecting high-birth-weight infants than the Hadlock II equation. Conclusions: It is clear that using 3DUS-VOCAL to measure FTV provides more accurate estimation of fetal birth weight.