Enter an RMS or peak-to-peak voltage to calculate the peak voltage of a sine wave.
How to Use the Peak Voltage Calculator
Toggle between "From RMS" and "From Peak-to-Peak" depending on which value is already on a meter or datasheet, enter that number, and the peak voltage updates immediately.
This calculator assumes a sine wave, which is worth stating up front because the √2 factor below is specific to that waveform — a square wave, triangle wave, or anything distorted enough to matter has a different peak-to-RMS relationship entirely.
From RMS: Vpeak = Vrms × √2
From peak-to-peak: Vpeak = Vpp ÷ 2Standard 120 V mains, which is always quoted as an RMS figure, actually swings up to about 169.7 V at the top of each cycle — that's √2 ≈ 1.414 times the number printed on every outlet and appliance label. It's a common gotcha for anyone selecting capacitor voltage ratings or insulation clearances off the RMS spec alone: the circuit sees the peak, not the average-equivalent RMS number, at least twice every cycle.
A multimeter set to AC volts reads RMS by default — it's built to show the number that matches an equivalent DC voltage's heating effect, not the instantaneous swing. Peak voltage has to be derived from that reading, which is exactly what this page does.
For the full swing from bottom to top rather than zero to top, use the Peak-to-Peak Voltage calculator; for RMS from a known peak, the RMS Voltage calculator runs this relationship in reverse.