This paper uses numerical limit analysis to produce stability charts for rock slopes. These charts have been produced using the most recent version of the Hoek-Brown failure criterion. The applicability of this criterion is suited to isotropic and homogeneous intact rock, or heavily jointed rock masses. The rigorous limit analysis results were found to bracket the true slope stability number to within 79% or better, and the difference in safety factor between bound solutions and limit equilibrium analyses using the same Hoek-Brown failure criterion is less than 4%. The accuracy of using equivalent Mohr-Coulomb parameters to estimate the stability number has also been investigated. For steep slopes, it was found that using equivalent parameters produces poor estimates of safety factors and predictions of failure surface shapes. The reason for this lies in how these equivalent parameters are estimated, which is largely to do with estimating a suitable minor principal stress range. In order to obtain better equivalent parameter solutions, this paper proposes new equations for estimating the minor principal stress for steep and gentle slopes, which can be used to determine equivalent Mohr-Coulomb parameters.