Physics Formulas

Root Mean Square

In physics, the root mean square or rms value of an alternating current or potential difference is not the same as the root mean square used in math calculations.

Definition of root mean square in physics

The root mean square value is the value of the direct current or potential difference that would give the same power dissipation as the alternating current or potential difference in a given resistor.

The term 'alternating' can be taken to include not only sine wave signals but any other regular waveform such as a square wave signal or a triangular wave form.

Root mean square value calculation formula

Root Mean Square

for sine wave only.

Representing sine wave signals can be either by:

1) graphs of y = instant value, x = time or

2) an equation of the form:

Root mean square formula


  • I = current at time t (A)
  • I0 = peak current (A)
  • f = frequency (Hz)

3) rotating vectors sometimes called phasors.