Current codes of practice can estimate the reduced capacity of compression members due to local buckling under ambient conditions, but the results of this study indicate that these codes, especially the American one, do not adequately predict the buckling capacity of steel plates at elevated temperatures. This paper proposes new and simple equations to calculate the buckling capacity of steel plates at elevated temperature. The approach modifies existing stress-based methods specified by American (AISC) and European (Eurocode) codes to account for steel material non-linearities at high temperature as well as reductions of strength and stiffness. A parametric study of ultimate plate strength was performed via finite-element analysis to obtain curves describing the relationship of critical stress to plate slenderness. The proposed equations are validated by comparison to these finite element analyses, and comparisons are also made to the AISC and Eurocode predictions.