Abstract: It is vital that horse owners, managers and veterinarians can accurately establish the weight of the horses in their care. The factors influenced by a horse’s weight include drug dosage, ration formulation, racing performance and transportation. The most accurate method of assessing the weight of a horse is a weighbridge. However, since the cost of this is prohibitive to most horse enterprises other methods usually are employed. Different method is available to estimate the weight of horses. After the weighbridge the best methods is weight formulas. In this study 4 formulas was compared by the Iranian Arab horse data. Measurements of girth, height and length were recorded on 244 horses. Effect of birth year and origin on different formulas was very significant (p<0.01). Effect of sex on different formulas was not significant (p>0.05). About 4 formulas that used in this study with Duncan test was classified to three classes.