Data collected on 43 steers (25 predominantly Hereford breeding (H) and 18 predominantly Angus breeding (A)) were used to generate equations to predict total body composition of Angus and Hereford steers from measurements obtained at slaughter. Empty body fat (ether extract, EBF), kg was predicted from 9–11 rib cut fat (ether extract, RF), kg and warm carcass weight (WCW), kg by the following: H — steers, EBF = − 11.49 + 44.08 RF + 0.22 WCW (R2 = 0.96, CV = 10.07%) and A — steers, EBF = − 49.30 + 31.30 RF + 0.50 WCW (R2 = 0.94, CV = 9.40%). Total empty body energy (EBE) (Mcal) was predicted from 9–11 rib cut energy (RE, Mcal) and WCW (kg) by the following: H — steers, EBE = − 252.6 + 28.85 RE + 4.26 WCW (R2 = 0.94, CV = 10.15%) and A — steers, EBE = − 434.3 + 25.48 RE + 5.64 WCW (R2 = 0.94, CV = 8.02%). Prediction of EBF and EBE from RF and RE, respectively, differed (P = 0.05) between breeds whereas prediction from WCW did not. For all steers, EBF, kg and EBE, Mcal, respectively, were predicted from WCW, kg, by the following: EBF = − 63.71 + 0.704 WCW (r2 = 0.91, CV = 12.44%) and EBE = − 537.7 + 7.377 WCW (r2 = 0.92, CV = 10.0%). Body protein (BP), kg was predicted from WCW, kg by the following: H — steers, BP = 23.31 + 0.154 WCW (r2 = 0.83, CV = 6.04%) and A — steers, BP = 11.32 + 0.195 WCW (r2 = 0.93, CV = 5.29%). Prediction of BP was not significantly improved by the inclusion of 9–11 rib protein in the equation with WCW. Prediction of body water and ash from weights of rib cut water and ash, respectively, and warm carcass weight were unacceptable. Non-linear relationships between rib cut component weights and corresponding empty body weights as well as between WCW and empty body component weights were generally not significant (P = 0.05). Inclusion of kidney and pelvic fat weight in these equations did not greatly improve their accuracy.