PWM Average Voltage Calculator
Pulse-width modulation controls the power delivered to a load by switching the supply on and off rapidly and varying the fraction of time it is on. The duty cycle sets the average voltage that a slow load or a low-pass filter sees. This calculator takes the supply voltage, the duty cycle, and the switching frequency, and returns the average output voltage, the RMS voltage for a resistive load, and the on-time and off-time within each switching period. All formulas assume an ideal two-level waveform.
PWM voltage formula
d = duty cycle percent / 100
Average voltage = Vsupply * d
RMS voltage = Vsupply * sqrt(d)
Period = 1 / frequency
On-time = Period * d; Off-time = Period * (1 - d)
The average is the time-weighted mean of the two levels. The RMS uses the square root of the duty cycle because the squared waveform is high only for the fraction d of each period. Times are converted to milliseconds for display.
PWM facts
- Average voltage scales linearly with duty cycle.
- RMS voltage scales with the square root of duty cycle.
- At 50 percent duty the RMS is about 0.707 of the supply, not 0.5.
- Higher switching frequency lets smaller filters smooth the output.
- Resistive heating in a load follows the RMS value, not the average.
PWM average voltage: frequently asked questions
How do I find the average voltage of a PWM signal?
For an ideal pulse-width-modulated signal that switches between the supply voltage and zero, the average voltage equals the supply voltage times the duty cycle expressed as a fraction. A 5 volt supply at 60 percent duty cycle averages 3 volts. This is the value a low-pass filter or a slow load such as an LED or motor responds to.
What is the RMS voltage of a PWM signal?
For an ideal two-level PWM waveform between the supply voltage and zero, the RMS voltage equals the supply voltage times the square root of the duty cycle fraction. RMS matters for power into a resistive load, because heating depends on the RMS value, not the average.
How are on-time and off-time calculated?
The period is one divided by the switching frequency. On-time equals the period times the duty cycle fraction, and off-time is the period minus the on-time. A 1 kHz signal at 25 percent duty has a 1 millisecond period, 0.25 milliseconds on, and 0.75 milliseconds off.
Does duty cycle of 0 or 100 percent make sense?
Yes. At 0 percent the output is always off, giving zero average and RMS voltage. At 100 percent the output is always on, equal to the full supply voltage for both average and RMS. The calculator accepts any duty cycle from 0 to 100 percent.
Why does my motor or LED respond to the average?
Inertia and thermal mass make many loads respond to the time-averaged value rather than the instantaneous switching. A motor's mechanical inertia smooths the pulses, and an LED's brightness over a period tracks the average current. The switching frequency is chosen high enough that the load cannot follow individual pulses.
Official sources
- NIST: Physical Measurement Laboratory: RMS and average waveform metrics.
- IEEE: IEEE standards for pulse-width modulation terminology.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.