Root Mean Square (RMS)

Definition of Root Mean Square (RMS)

The most common method or specifying the amount of a sine wave of voltage or current is by relating it to dc voltage and current that will produce the same heating effect.  This is called its root-mean-square value, abbreviated rms.

Formula for RMS:

  • RMS Value = 0.707 × Peak Value


Or we can say

  • Vrms = 0.707 Vmax    and Irms = 0.707 Imax  


For example:

With a peak of 170 V, the sine value is 0.707 × 170, or 120 V, approximately.  This is a voltage of the commercial ac power line, which is always given in RMS value.

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