4W RMS total output power
RMS refers to Root Mean Square which is a typical measurement of audio power, or rather, the electrical power transferred from an audio amplifier to a loudspeaker, which is measured in watts. The amount of electrical power delivered to the loudspeaker and its sensitivity determines the sound power that is generated. Essentially, amplifiers are limited by the electrical energy they can amplify and loudspeakers by the electrical energy they can convert into sound energy, without distorting the audio signal. The higher the wattage, the better the sound power emitted by the speaker.