RMS Voltage Calculator
Convert between RMS, peak, peak-to-peak, and average voltage for sine waves.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
Can't find what you need?
Request a ToolHow to Use the RMS Voltage Calculator
AC voltage is described by several different values. This calculator converts between them instantly for pure sine waves.
- Select your input type. Choose whether your known value is RMS, Peak, or Peak-to-Peak voltage.
- Enter the voltage. Type the voltage value in volts.
- Read all four values. The calculator outputs RMS, Peak, Peak-to-Peak, and average voltage simultaneously.
Common use cases: oscilloscopes measure and display peak or peak-to-peak voltage. Multimeters display RMS voltage. Power calculations use RMS. Transformer datasheets may list peak secondary voltage. This calculator quickly converts between these representations.
About RMS Voltage
For a pure sine wave: Vpeak = Vrms × √2. Vpp = 2 × Vpeak = 2√2 × Vrms. Average (full-wave rectified) = Vpeak × 2/π ≈ 0.637 × Vpeak. The RMS voltage is the DC equivalent in terms of heating power: a 120 Vrms AC supply heats a resistor the same as 120 V DC.
US household voltage is 120 Vrms (approximately 170 V peak, 340 V peak-to-peak). European voltage is 230 Vrms (approximately 325 V peak). These RMS values are what drives the heating, motors, and other loads — the peak values only matter for component voltage ratings (capacitors, semiconductors, cable insulation).
Frequently Asked Questions
What is RMS voltage and why is it used?
RMS (Root Mean Square) voltage is the effective value of an AC voltage — the DC equivalent that would produce the same heating power in a resistor. For a sine wave, Vrms = Vpeak / √2 ≈ 0.707 × Vpeak. It is the standard way to specify AC voltages because it directly relates to power: P = Vrms² / R. This is why household voltage is rated 120 or 230 Vrms rather than peak values.
What is the peak voltage of US household 120V AC?
US household voltage is 120 Vrms. The peak voltage is 120 × √2 ≈ 169.7 V. The peak-to-peak voltage is approximately 339.4 V. This matters for component selection: capacitors and other components connected to the AC line must be rated well above 170 V, which is why 200 V or 250 V rated components are commonly used in line-voltage circuits.
Does this calculator work for non-sine wave signals?
No. The relationships Vrms = Vpeak/√2 and Vavg = Vpeak × 2/π apply only to pure sine waves. For square waves, Vrms = Vpeak (at 50% duty cycle). For triangle waves, Vrms = Vpeak/√3. For other waveforms, RMS must be calculated by integrating the square of the instantaneous voltage over one cycle. True-RMS multimeters measure RMS directly regardless of waveform shape.
Why does my oscilloscope show a different voltage than my multimeter?
Oscilloscopes typically display peak or peak-to-peak values. Standard (non-true-RMS) multimeters display RMS, but calculate it by multiplying the average (rectified) value by a fixed correction factor of 1.11, which only works for pure sine waves. A true-RMS multimeter computes RMS correctly for any waveform. If your AC signal is not a clean sine wave (e.g., a PWM signal or distorted mains), expect discrepancies between readings.