Earlier studies of the depths of geophysical boundary layers basically focused of the effects of rotation and density stratification. One more inherent feature of geophysical flows, namely the fact that they are nearly always baroclinic rather than barotropic, was not taken into account in the known formulations. The present paper makes up for this deficiency. A new equation for the neutral baroclinic Ekman boundary-layer depth is derived and validated against data from large eddy simulations (LES). The latter are generated using a new code specifically designed for modelling of neutral and stable boundary layers. Results from the comparison show an excellent correspondence between the proposed equation and LES data.