The objective of this research was to determine the rib eye area (REA) and back fat thickness (BFT) between the 12th and 13th rib, using real-time ultrasound for estimating the yield of total meat produced (YTMP), total meat produced (TMP), yield grade (YG), adjusted yield grade (AYG) and commercial cuts (CC) in a dual-purpose grazing bulls in the tropic to obtain an equation to estimate the hot carcass weight (HCW). Thirty-seven crossbred Holstein/Zebu (Ho/Z) and Brown Swiss/Zebu (BS/Z) bulls were subjected to ultrasound images prior to slaughter at the time when their weight was between 300 and 500 kg. Mean REA and BFT were 76.02 cm² and 3.6 mm respectively in comparison to 77.38 cm² (REA) and 4.0 mm (BFT) in the ultrasound. The TMP estimated by ultrasound scan did not differ between genotypes and at different slaughter weights. YTMP was better (P<0.05) for animals over 450 kg. The YG value was close to 1.0 with 52-54% of CC without significant effect on genetic group and slaughter weight. AYG values of 2 and 50-52% of CC was obtained. With the developed prediction equation HCW (kg) = - 338 + 2.48 carcass length +2.30 carcass width + 2.79 leg depth) r² = 0.92 and the goodness of fit test was assessed with χ² without significant difference (P>0.05). The results indicated that ultrasound image may give an estimate of rib eye area (UREA) and back fat thickness (UBFT).