Clock Duty Cycle Calculator
Calculate any two of frequency, period, duty cycle, or high/low times. Shows a live waveform with the timing marked out.
How to Use
- Enter any two of: frequency, period, duty cycle percentage, tHigh, or tLow.
- The remaining values compute automatically.
- Waveform preview updates live, showing the on/off windows.
- Common PWM duty cycles: 0% = off, 50% = square wave, 100% = on.
Show Work
Formulas
About Duty Cycle
Duty cycle is everywhere in electronics. Digital clocks typically run at 50% for balanced rise/fall timing. PWM signals span 0-100% for variable control of motors, LEDs, and switching regulators. Servo signals use extreme duty cycles (5-10%) in a fixed 50Hz period.
Beware of asymmetric duty in digital clocks: a 30/70% duty cycle still has the right frequency, but setup/hold margins are cut in half on one half-cycle. Clock synthesizers and crystal oscillators always output near 50% duty for this reason.
History of Clock Signals and Duty Cycle
The concept of a duty cycle predates electronics — it originated in steam-engine terminology of the 1800s, describing the fraction of a piston stroke during which steam was admitted. The term migrated to electrical machinery in the 1900s (motor duty cycles: continuous, short-time, intermittent), then to pulse electronics during WWII radar development. Radar PRF (pulse repetition frequency) and duty cycle directly governed average transmitter power and range ambiguity.
Digital clock signals converged on ~50% duty in the 1970s as TTL became dominant. Setup and hold times specify how long data must be stable before and after a clock edge; asymmetric duty effectively shortens one of those windows. Modern DDR4 memory actually uses both edges (dual-edge triggering) for 2× data rate, making clock duty accuracy a first-class signal-integrity parameter — typical DDR4 spec is 45-55%.
PWM for power control exploded in the 1980s with the MOSFET revolution: switching an FET at 20-100 kHz with variable duty lets a DC bus drive motors, LEDs, solenoids, and power supplies with near-zero switch loss. Today PWM dominates drive electronics from million-volt rail traction inverters to milliamp phone vibrator motors.
About This Calculator
Enter any two of: frequency, period, duty cycle, tHigh, tLow. The tool solves for the rest using T = 1/f, D = tH/T, tL = T − tH. Units with SI prefixes parse automatically (kHz, MHz, µs, ns). The waveform visualization shows one period at scale with the on/off windows marked.
Common gotchas: servo signals use 20 ms period (50 Hz) with 1-2 ms pulse width, which is 5-10% duty — not a 5 Hz signal. LED PWM should stay above ~200 Hz to avoid visible flicker for moving eyes; 1 kHz is a safe default. Motor PWM typically runs 16-25 kHz (above hearing). Everything runs client-side; no values leave your browser.
About the Clock Duty Cycle Calculator
The Clock Duty Cycle Calculator is a free tool for electronics and circuit design. It runs right in your web browser, so there is nothing to download. Calculate any two of frequency, period, duty cycle, or high/low times. Shows a live waveform with the timing marked out.
How it works
Type your numbers into the boxes. The answer shows up right away — you do not have to press a button. If you change a number, the answer changes too. So you can try different numbers and watch what happens, or check an answer you worked out yourself. Just make sure each box has the right kind of number in it.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
What is duty cycle?
The fraction of one period during which the signal is high, expressed as a percentage. 25% duty means the signal is high 25% of each cycle, low 75%. A square wave is 50% duty.
Frequency vs period?
They\'re reciprocals. f = 1/T. Frequency (Hz) is cycles per second; period (seconds) is time per cycle. A 1kHz clock has a 1ms period.
When does duty cycle matter?
In PWM (pulse-width modulation) for motor speed, LED brightness, power delivery. Also in digital clocks where very asymmetric duty can cause setup/hold violations. Most digital gear expects 40-60% duty.
How is tHigh different from duty?
Duty is a percentage; tHigh is an absolute time. t_high = D × T. A 50% duty cycle at 1 kHz means tHigh = 500µs; at 10 kHz it means tHigh = 50µs.
How do I use the Clock Duty Cycle Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
PWM Motor Control
Drive a DC motor at 10kHz PWM with 75% duty for 3/4 full-speed operation.
LED Dimming
Run LEDs at 1kHz PWM with 20% duty for an easily-perceived 20% brightness without flicker.
Clock Signal Analysis
Measuring a 100MHz CPU clock on a scope — verify duty is close to 50% for clean timing.
Servo Signal
R/C servos expect a 20ms period (50Hz) with 1-2ms pulse (5-10% duty) encoding position.
Audio Waveform Generation
Synthesize a square wave at 440Hz (A4 note) for basic tone generation.
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