RMS (root mean square) voltage is the effective value of an AC voltage — the equivalent DC voltage that would deliver the same average power to a resistive load. For a 120 V RMS mains supply, the peak voltage is about 170 V.

How is V_rms calculated for a sine wave?

For a pure sine wave, V_rms = V_peak / sqrt(2) ≈ V_peak × 0.7071. Equivalently, V_rms = V_pp / (2 × sqrt(2)) ≈ V_pp × 0.3536.

Why does waveform shape matter?

Different waveforms have different crest factors (V_peak / V_rms). A square wave has a crest factor of 1 (V_rms = V_peak), a triangle wave is 1/sqrt(3) ≈ 0.5774 × V_peak, and a sawtooth is the same as a triangle. Choosing the wrong shape gives an incorrect RMS result.

What is peak-to-peak voltage?

Peak-to-peak voltage (V_pp) is the total voltage swing from the negative peak to the positive peak of a waveform. For a symmetric waveform, V_pp = 2 × V_peak.

What is the crest factor?

The crest factor is the ratio of V_peak to V_rms. A lower crest factor means the waveform is more efficient at delivering power. A square wave (crest factor = 1) is the most efficient; a sine wave has a crest factor of sqrt(2) ≈ 1.414.

RMS Voltage Calculator

Convert between peak, peak-to-peak, and RMS voltage for common AC waveforms instantly.

Input

Waveform Type

Known Voltage

Voltage Value

Results

Enter a voltage value to see results.

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Summary

RMS (root mean square) voltage is the effective DC equivalent of an AC waveform — the value that delivers the same power to a resistive load. This calculator converts between peak voltage (V_peak), peak-to-peak voltage (V_pp), and RMS voltage (V_rms) for four common waveform shapes. For a sine wave, V_rms = V_peak / sqrt(2) ≈ 0.7071 × V_peak. Other waveforms use different crest factors.

How it works

Select the waveform type (sine, square, triangle, or sawtooth).
Choose your known input: peak voltage or peak-to-peak voltage.
Enter the voltage value in volts.
The calculator instantly shows V_rms, V_peak, V_pp, and the crest factor.
Results update in real time as you type.

Use cases

Convert mains AC voltage between peak and RMS values.
Verify oscilloscope peak readings against expected RMS values.
Size components (capacitors, MOSFETs) based on peak voltage stress.
Calculate crest factor for power supply design.
Compare waveform types in signal processing and audio electronics.
Determine safe operating margins for AC circuits.

Frequently Asked Questions

Last updated: 2026-05-28 · Reviewed by Nham Vu