Calculators
Duty Cycle Calculator
Calculate PWM duty cycle, pulse width, frequency, period, and off-time.
Calculate PWM duty cycle, period, frequency, pulse width, and off-time from either frequency plus duty cycle or measured high and low pulse times.
Duty cycle25%
Frequency1 kHz
Period1 ms
High time / pulse width250 µs
Low time750 µs
This calculator describes an ideal repeating two-state waveform. It does not account for rise/fall time, jitter, dead time, modulation changes, or hardware switching limits.
About This Tool
Duty cycle describes what fraction of each repeating signal period is spent in the high or active state. It is commonly used with PWM motor control, LED dimming, switching converters, clocks, timers, and digital pulse measurements. This calculator works in both directions: enter frequency and duty cycle to find pulse width and low time, or enter measured high and low times to find duty cycle, period, and frequency. All calculations run locally in your browser and use the ideal timing relationships for a repeating two-state waveform.
How To Use It
- Choose Frequency + duty cycle when you know the repetition frequency and percentage of each cycle that is high.
- Choose High + low time when you measured the on-time and off-time of one complete pulse cycle.
- Select the appropriate engineering unit. Frequency inputs support Hz, kHz, and MHz; pulse-time inputs support seconds through nanoseconds.
- Read the calculated duty cycle, frequency, period, high time, and low time together so you can check the complete timing relationship.
Examples
1 kHz PWM at 25% duty
A 1 kHz signal has a 1 ms period. At 25% duty cycle, it is high for 250 µs and low for 750 µs each cycle.
2 ms high and 6 ms low
The total period is 8 ms, so frequency is 125 Hz. The high state occupies 2/8 of the period, giving a 25% duty cycle.
50% square-wave timing
At 50% duty cycle the ideal high and low times are equal. A 10 kHz signal therefore has a 100 µs period with 50 µs high and 50 µs low.
Useful Notes
Duty cycle formula
Duty cycle D = (t_high / T) × 100%, where t_high is the time spent high and T is the complete period. Because T = t_high + t_low, measured high and low times can directly determine the duty cycle.
Frequency and period
Frequency and period are reciprocals: f = 1/T and T = 1/f. A 1 kHz waveform repeats 1,000 times per second, so one ideal period lasts 1 ms.
Pulse width from PWM frequency
For a known frequency and duty cycle, high time is T × D/100 and low time is T minus high time. Pulse width often refers to this high-time interval, although terminology can vary by system.
0% and 100% duty cycle
The mathematical timing model permits 0% and 100%: the high time becomes zero at 0%, while the low time becomes zero at 100%. Some real PWM peripherals cannot generate these endpoints exactly or treat them as special constant-output states.
Real waveform limitations
Physical signals do not switch instantaneously. Rise time, fall time, jitter, propagation delay, dead time, minimum pulse width, timer resolution, and load behavior can make measured or usable timing differ from the ideal values.
Using the result
Use these results for timing checks and learning, then compare them with the timer, PWM peripheral, driver, switch, or load specifications when designing real hardware. A valid arithmetic duty cycle does not guarantee that a device can switch at the requested timing.
FAQ
What does 25% duty cycle mean?
It means the signal is high for one quarter of each complete period and low for the remaining three quarters.
How do I calculate pulse width from frequency?
First find period with T = 1/f, then multiply the period by duty cycle divided by 100. For example, 1 kHz at 25% gives 1 ms × 0.25 = 250 µs.
Is duty cycle the same as frequency?
No. Frequency tells how often the waveform repeats; duty cycle tells what percentage of each repetition is spent high.
Does this calculate average PWM voltage?
No. This tool focuses on timing. Average voltage or delivered power depends on waveform levels, load behavior, switching circuitry, and filtering, so it should not be inferred from duty cycle alone without the appropriate circuit model.
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