A power-measuring device serves to measure the power of a three-phase system. It comprises a measuring unit for measuring a power of a first phase of the three-phase system, a display unit for displaying measured results and an operating unit for the operation of the power-measuring device by a user. Furthermore, it comprises a communications unit by means of which it can communicate with one or more further power-measuring devices. In this context, the power-measuring device is embodied, jointly with the one or more further power-measuring devices, to measure a power of several phases of the three-phase system.