Seismic performance of reinforced concrete (RC) columns should be evaluated considering biaxial demands for a more realistic assessment. However, most of the current seismic assessment regulations stipulate rotation capacity estimations considering only uniaxial bending test database. The effect of seismic demands in one direction may have a detrimental effect in the deformation capacity of the other direction. In the past studies, the influence of biaxial loading patterns/paths/histories, axial load level, and cross section shape on seismic performance of RC columns were evaluated by examining the lateral strength, stiffness, rotation capacity, ductility, and energy dissipation capacity. No systematic investigations were made for estimating biaxial rotation capacities. A database of 196 RC columns (138 biaxially loaded and 58 uniaxially loaded companion columns) was compiled to study the accuracy of existing plastic rotation capacity models. Eurocode 8-3 and ASCE/SEI 41-17 were observed to overestimate the column rotation capacities under biaxial effects. However, TBEC-2018 recommendations were shown to give the over safe predictions with a higher dispersion. Simple expressions were recommended in order to predict the plastic rotation and rotation capacity of RC columns by using a circular failure envelope considering the confinement ratios in both directions and the axial load ratio. The suggested formulations were shown to give close results to experimental rotations with less standard deviation compared to the examined models.