Weight tapes and body weight estimation formulas are routinely used to determine the body weight of domestic mammals when a scale is not available. A sample of 145 animals (79 females and 66 males) of different ages (from sucklings to very old individuals) and from different flocks, from different local communities of the Chiapas Department in SE Mexico, were measured for thoracic girth (TG), knee perimeter (forelimb), fetlock perimeter (forelimb), cannon perimeter (at the forelimb just below the knee), ankle perimeter and ear length. Measurements were obtained with a flexible tape by the same person, and weighed. Live weight (LW) was estimated using a linear model. Coefficient of determination (R2) values computed for the body for thoracic girth was 0.874. It was concluded that chest girth is a useful tool in predicting weight of indigenous Chiapas sheep. The predictive equations for the live weight determination from thoracic girth, LW (kg) = TG0.730 and LW (kg) = TG0.696 (TG expressed in cm) for males and females respectively, can be considered satisfactory. This represents a quite simple formula, easy to remember, presenting a high coefficient of determination and no differences between real and estimated weight values, so it could be adopted as a good body weight estimation for all ages and for sexes independently.