People tend to grossly overestimate the size of their mirror-reflected face. Although this overestimation bias is robust, not much is known about its relationships to self-face perception. In two experiments, we investigated the overestimation bias as a function of the presentation of the own face (left-right reversed - as in a mirror - or nonreversed - as in a photograph), the identity of the seen face, and prior exposure to a real mirror. For this we developed a computerized task requiring size estimations of displayed faces. We replicated the observation that people overestimate the size of their mirror-reflected face and showed that the overestimation can be reduced following a brief mirror exposure. We also found that left-right reversal modulates the overestimation bias, depending on the perceived face's identity. These data underline the enhanced familiarity of left-right reversed self-faces and the importance of size perception for understanding mirror reflection processing.