Root mean square, RMS, rms, is the square root of the arithmetic mean of the squares of the values. For continuous waveforms and AC power source voltage values, RMS values are usually used. For example, the alternating current (AC) supplied by the concessionaire is labeled 100 V, but it is actually 100 Vrms, and the difference between the minimum and maximum voltage is 141 volts. The difference between the maximum and minimum amplitudes is called peak to peak. ( See peak to peak.)

The root-mean-square is used in electronics and physics to evaluate the amplitude of waves and to express the effective value of alternating current (AC), as well as for tolerance analysis in quality control.