What do you mean about the Root Mean Square Voltage?
Root mean square voltage is written as Vrms. RMS voltage is a method to denoting a voltage sine waveform as an equivalent DC voltage that will produce the same amount of heat or power dissipated from the circuit, as in the AC voltage.
Consider a load resistor connected with the DC voltage 5v. We need a 0.05watt power across the resistor, Now we say that current flow through the resistor is 10mA. Now we connect the entire circuit to the Ac voltage source. The same amount current flow through the resistor with the RMS voltage 5, then we can use the peak voltage approximately 7.07v is useful to get the exact amount of power.
Vrms = Vpeak *0.707
Vpeak = Vrms*1.414
Vrms = Vpp*0.3535
Vrms = Vavg*1.1107