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RMS Voltage Calculator
Pick a waveform, enter any one of peak, peak-to-peak, RMS or average voltage, and get all the others instantly. The calculator also shows the crest factor, form factor, what an average-responding meter would read, and an optional current and power for a resistive load.
Last updated:
Waveform
V
Hz
Used for the period and the waveform plot
Ω
Adds RMS current and average power
Enter your values to see the result.
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How to use the RMS Voltage Calculator
- Choose the waveform you are measuring.
- Select which value you know: peak, peak-to-peak, RMS or average.
- Enter the voltage and, if you like, the frequency and a load resistance.
- Read the converted values, crest factor and form factor.
- Compare waveforms in the table to see how the same reading differs between wave shapes.
Waveform conversion factors
| Waveform | Vrms | Vavg | Vpp | Crest factor | Form factor |
|---|---|---|---|---|---|
| Sine | Vp ÷ √2 = 0.7071 Vp | 2Vp ÷ π = 0.6366 Vp | 2 Vp | 1.4142 | 1.1107 |
| Square (50% duty, ±Vp) | Vp | Vp | 2 Vp | 1 | 1 |
| Triangle | Vp ÷ √3 = 0.5774 Vp | Vp ÷ 2 | 2 Vp | 1.7321 | 1.1547 |
| Sawtooth | Vp ÷ √3 = 0.5774 Vp | Vp ÷ 2 | 2 Vp | 1.7321 | 1.1547 |
| Half-wave rectified sine | Vp ÷ 2 | Vp ÷ π = 0.3183 Vp | Vp | 2 | 1.5708 |
| Full-wave rectified sine | Vp ÷ √2 | 2Vp ÷ π = 0.6366 Vp | Vp | 1.4142 | 1.1107 |
For the symmetrical AC waves, the average is the rectified average (the mean of the absolute value). The plain mathematical average over a full cycle is zero. All values assume no DC offset.
Common mains voltages
| Nominal (RMS) | Peak | Peak-to-peak | Frequency |
|---|---|---|---|
| 100 V | 141.4 V | 282.8 V | 50/60 Hz |
| 120 V | 169.7 V | 339.4 V | 60 Hz |
| 230 V | 325.3 V | 650.5 V | 50 Hz |
| 240 V | 339.4 V | 678.8 V | 50/60 Hz |
| 480 V (line-to-line) | 678.8 V | 1,357.6 V | 60 Hz |
Tips
- Oscilloscope readings are usually peak-to-peak. Divide by 2 for the peak, then apply the waveform factor for RMS.
- Insulation and component ratings must handle the peak voltage, not just the RMS value. A 230 V circuit sees about 325 V at every peak.
- Power calculations always use RMS values: P = Vrms × Irms for a resistive load.
- Square waves with other duty cycles (for example PWM from 0 to Vp) have Vrms = Vp × √D and an average of Vp × D, where D is the duty cycle.
Frequently asked questions
How do I convert peak voltage to RMS?
For a sine wave, divide the peak voltage by √2: Vrms = Vp × 0.7071. For a symmetrical square wave the RMS equals the peak, and for a triangle or sawtooth wave Vrms = Vp ÷ √3 = Vp × 0.5774.
What is the peak voltage of 120 V AC mains?
Household voltage is quoted as RMS. A 120 V RMS sine wave has a peak of 120 × √2 ≈ 169.7 V and a peak-to-peak value of about 339.4 V. For 230 V mains the peak is about 325.3 V.
What does RMS voltage mean?
RMS (root mean square) is the DC voltage that would deliver the same average power to a resistor. It is found by squaring the waveform, averaging over one period and taking the square root, which is why it is the value used for power calculations: P = Vrms² ÷ R.
What is the average voltage of a sine wave?
Over a full cycle the average of a symmetrical sine wave is zero, so the quoted average is the rectified (half-cycle) average: Vavg = 2Vp ÷ π ≈ 0.6366 Vp. For a half-wave rectified sine the DC average is Vp ÷ π ≈ 0.3183 Vp.
What are crest factor and form factor?
Crest factor is peak ÷ RMS (√2 ≈ 1.414 for a sine, 1 for a square wave, √3 ≈ 1.732 for a triangle). Form factor is RMS ÷ average (about 1.1107 for a sine, 1 for a square, about 1.1547 for a triangle).
Why does my multimeter read wrong on a square or triangle wave?
Many basic meters measure the rectified average and multiply by 1.1107, the sine-wave form factor. That gives the correct RMS only for sine waves. On a square wave such a meter reads about 11% high and on a triangle wave about 3.8% low. A true RMS meter avoids this error.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.
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