This study took place in a cattle ranch working with double-purpose cattle, in the Department of Jutiapa, Guatemala, with the objective of calibrating a model of cattle measuring tape, with body measures, during the months of April, May and July, 1993. The measures were taken from 456 cattle heads, and the measuring variables comprehended: the torax diameter (TD), the body lenghth (BL), the live weight in kilograms (LW), and the age in years (AG). Cattle food was mainly pastures of “African Star” and “Jaragua” varieties, and other natural species. The herd produces milk all year round with a daily milking, and calves suckle until eight months old. The cattle measurements information was analyzed throughout fixed-effect models, including the TD, BL and AG variables, to determine the contribution of each effect for the live weight predictions. Two lineal multiple regressive models were adjusted by natural logarithm and by base-10 for males and females respectively. The analysis determined that in the studied population, the TD, BL and AG variables can be used to predict the live weight, according to the animal’s sex.