PWM Duty Cycle Calculator

Work out pwm duty cycle instantly with clear inputs, formula shown and shareable results.

About PWM Duty Cycle Calculator

Duty cycle is on time divided by period. The average voltage of a PWM waveform is supply times duty, but the RMS value is supply times the square root of duty — the distinction matters because heating in a resistive load follows RMS, not average.

Formula

PWM

duty = ton / T; Vavg = Vs x duty; Vrms = Vs x sqrt(duty)

Worked example

With the default values below, PWM Duty Cycle Calculator returns Duty cycle of 30.000%. Change any input above and every figure here is recalculated in your browser.

Inputs used

On time: 1.2 ms
Period: 4 ms
Supply voltage: 12 V

Results

Duty cycle: 30.000% %
Frequency: 250.00 Hz
Average output voltage: 3.6000 V
RMS output voltage: 6.5727 V

Step by step

1Values used
2PWM
3Duty cycle= 30.000 %
4Frequency= 250.00 Hz
5Average output voltage= 3.6000 V
6RMS output voltage= 6.5727 V

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Why does a heater at 50% duty not get half as hot?

Because power follows the square of RMS voltage. At 50% duty the RMS voltage is 0.707 Vs, giving exactly half the power, which is correct — but the average voltage of 0.5 Vs would predict only a quarter.

Does PWM frequency matter?

Yes. It must be well above the load's response time: kilohertz for motors, tens of kilohertz to avoid audible noise, and much higher for LED dimming without flicker.