This paper evaluates the potential capacity improvements in mobile radio systems due to perceptual-based power control. It builds on our previous work on the application of a Real-time Perceptual Speech Quality Metric (RTPSQM) in power control. Encouraged by the performance improvements offered with perceptual-based power control, this paper investigates on how gains in average transmitter power and SIR target translate to gains in the actual capacity in the Global System for Mobile communication (GSM) and the Universal Mobile Telecommunication System (UMTS). In particular, capacity improvements in terms of number of users per cell between 25% to 91% are obtained for perceptual-based power control in GSM. As for UMTS, the results show an increase in Erlang capacity per cell by at least 10%.