RMS vs Peak
Peak, peak-to-peak, average, and RMS voltage relationships for common waveforms.
Reference
Sine wave
- V_peak
- Amplitude of the waveform
- V_pp
- = 2 · V_peak (peak-to-peak)
- V_avg (abs)
- ≈ 0.637 · V_peak
- V_RMS
- = V_peak / √2 ≈ 0.707 · V_peak
- Crest factor
- = V_peak / V_RMS = √2 ≈ 1.414
- Form factor
- = V_RMS / V_avg ≈ 1.11
Common waveforms
| Waveform | V_RMS / V_peak | V_avg / V_peak | Crest factor |
|---|---|---|---|
| Sine | 0.707 (1/√2) | 0.637 (2/π) | 1.414 |
| Full-wave rect. | 0.707 | 0.637 | 1.414 |
| Half-wave rect. | 0.500 | 0.318 | 2.000 |
| Square | 1.000 | 1.000 | 1.000 |
| Triangle | 0.577 (1/√3) | 0.500 | 1.732 |
| Sawtooth | 0.577 | 0.500 | 1.732 |
| White noise | — | — | ~3.0–4.0 |
Mains examples
- 120 V RMS (US)
- V_peak ≈ 170 V, V_pp ≈ 340 V
- 230 V RMS (EU)
- V_peak ≈ 325 V, V_pp ≈ 650 V
- 277 V RMS (US industrial)
- V_peak ≈ 392 V
Notes
- RMS is the DC-equivalent heating value: an RMS current through a resistor dissipates the same average power as that DC value.
- Only true-RMS meters report correct RMS on non-sinusoidal signals (PWM, dimmers, switching supplies).
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