We studied the subjectively perceived intensity of the haptic feedback and the effects of the integration of the audio and haptic feedback. The purpose of the study was to specify design principles for haptic feedback on a piezo actuator enhanced mobile touch display device. The results of the study showed that the best corresponding physical parameter to perceived feedback intensity was the acceleration of the haptic stimulus pulse. It was also noticed that the audio stimuli was biasing the perception of the haptic stimuli intensity. These results clarify the principles behind haptic feedback design and imply that the multisensory integration should be stressed when designing haptic interaction.