AC foundations
Peak voltage
- where
- peak voltage (V)
- RMS voltage (V)
Explain this equation
Works out the peak voltage of a sine wave from its RMS value. Matters for insulation, component voltage ratings and rectifier outputs.
Vₚ is the peak voltage, the top of the wave. Vᵣₘₛ is the RMS voltage, the value meters show and supplies are quoted in.
RMS is the steady DC value that would give the same heating. For a pure sine wave, the peak is √2 (about 1.414) times that RMS value.
Sense check: 230 V RMS peaks at about 325 V. 400 V RMS peaks at about 566 V.
Watch out: the √2 only holds for a clean sine wave centred on zero. Distorted waveforms can have higher peaks.
For a sinusoidal voltage centred on zero, the peak is √2 times RMS. RMS indicates equivalent resistive heating.
This factor is tied to the sine-wave shape. A square wave or distorted waveform needs its own RMS calculation.
Enter your values to see the result.
Common mistake
Using √2 for every waveform.
Limits
Sinusoidal waveform with zero DC offset.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.