Background: To compare the accuracy of 18 formulas in predicting fetal weight and also to make a comparison of these formulas in low-birth-weight fetuses (<2,500 g) and in fetuses weighing >4,000 g. Methods: Four-hundred-and-ninety-five pregnant patients were enrolled. The estimated fetal weight was calculated using 18 different formulas. The mean percentage error, the mean absolute percentage error and reliability analysis were used to compare the performance of the formulas. Results: The Cronbach's alpha was the highest in the formulas Hadlock I (0.977 (95% CI = 0.972-0.980)), Hadlock III (0.977 (95% CI = 0.972-0.980)) and Ott (0.975 (95% CI = 0.970-0.979)) in all fetuses. It was the highest in formulas Ott (0.383 (95% CI = 0.091-0.581)), Hadlock IV (0.371 (95% CI = 0.074-0.572)) and Combs (0.369 (95% CI = 0.071-0.571)) in fetuses >4,000 g. It was the highest in formulas Coombs (0.957 (95% CI = 0.940-0.569)), Ott (0.956 (95% CI = 0.939-0.968)) and Hadlock IV (95% CI = 0.956 (0.938-0.968)) in fetuses <2,500 g. Conclusion: We noted that formulas Hadlock I, Hadlock III and Ott may be used to predict the estimated fetal weight accurately in all fetuses in our study. Formulas Ott, Hadlock IV and Coombs may be preferred to predict EFW in fetuses <2,500 g and >4,000 g. Better formulas should be developed to predict the fetal weight in fetuses >4,000 g.