Duty Cycle Calculator
Enter any two timing values (pulse width, period, or frequency) and get the duty cycle percentage instantly. Switch modes to work with average and peak power, calculate average PWM voltage, or solve for fuel injector duty cycle. The "Show your work" panel walks through every formula step by step.
Formula
Worked example
A PWM signal has a pulse width of 2 ms and a period of 10 ms. Duty cycle = (2 ms / 10 ms) x 100 = 20%. The frequency is 1 / 0.01 s = 100 Hz. If the supply voltage is 12 V, the average voltage at 20% is 2.4 V.
What is duty cycle?
Duty cycle is the proportion of one period that a signal, device, or system spends in an active (on) state. It is expressed as a percentage: 0% means the signal is never on, 100% means it is on all the time, and 50% means equal on and off time. The term appears in electronics, power engineering, mechanical engineering, and telecommunications with the same core meaning: the ratio of active time to total cycle time. A related dimensionless form called the duty factor expresses the same ratio as a decimal (for example, 0.20 instead of 20%).
Duty cycle formulas
The most direct formula uses pulse width (PW) and period (T): D = (PW / T) x 100. Because period and frequency are reciprocals, you can substitute f to get D = PW x f x 100 when you know frequency instead. For pulsed power systems, the power-ratio form is often more convenient: D = (P_avg / P_peak) x 100, which follows directly from the fact that average power equals peak power multiplied by the fraction of time the signal is active. In PWM circuits the average output voltage is V_avg = V_supply x (D / 100). Fuel injector duty cycle uses a slightly different form to account for how many times the injector fires per crankshaft revolution: IDC = (IPW x RPM) / 1200 for 4-stroke engines (where the factor 1200 = 60000 ms/min divided by 2 revolutions per firing event divided by 100 for the percentage).
Practical applications of duty cycle
Pulse-width modulation (PWM) is the most widespread application. A microcontroller drives a transistor at a fixed frequency but varies the duty cycle to control the effective voltage or power delivered to a motor, heater, or LED. A fan running at 30% duty cycle receives 30% of full power and spins proportionally slower. In automotive fuel injection, injector duty cycle tells tuners how much of the available firing window is consumed: staying below 80-85% leaves headroom and protects linearity. Radar systems use very short pulses with duty cycles often below 1% so the receiver can listen between transmissions. Welding power sources are rated by duty cycle over a 10-minute window: a 60% rated welder can arc for 6 minutes then must rest 4 minutes to avoid overheating. Understanding duty cycle ensures safe, efficient operation across all these domains.
How to use this calculator
Choose the mode that matches what you already know. Basic mode (pulse width plus period) is the most common starting point: enter the on-time and total cycle time in any time unit and the calculator returns duty cycle percentage, duty factor, off-time, and frequency. Frequency mode accepts pulse width and switching frequency directly. Power mode derives duty cycle from the ratio of average to peak power, useful for pulsed lasers and radar. PWM average voltage mode shows the effective voltage a PWM signal delivers and plots average voltage against duty cycle so you can pick the right percentage for your target voltage. Fuel injector mode converts RPM and injector pulse width into injector duty cycle for 4-stroke or 2-stroke engines. All modes display a step-by-step worked solution panel.
Duty cycle ranges and typical applications
| Duty cycle | Range | Typical applications | Risk level |
|---|---|---|---|
| Very low | 0-10% | Radar pulses, strobe lights, burst-mode lasers | Low |
| Low | 10-50% | PWM fan control, servo signals, LED dimming | Low |
| Moderate | 50-75% | Motor speed control, audio amplifiers | Moderate |
| High | 75-90% | Heating elements, actuators, solenoid valves | Elevated |
| Near-continuous | 90-100% | Continuous-rated devices only, welders at spec limit | High |
General industry guidelines. Always confirm against the component data sheet for the specific device.
Frequently asked questions
What does a 50% duty cycle mean?
A 50% duty cycle means the signal is HIGH for exactly half of each period and LOW for the other half. On-time equals off-time. Square waves used as clock signals in digital circuits often have a 50% duty cycle. For a PWM signal with a 12 V supply, 50% duty cycle delivers an average of 6 V to the load.
What is the difference between duty cycle and duty factor?
They express exactly the same thing in different scales. Duty cycle is a percentage (e.g. 25%), and duty factor is the same value as a dimensionless decimal (0.25). To convert duty factor to duty cycle, multiply by 100. The duty factor form is convenient in power calculations because average power equals peak power multiplied directly by the duty factor.
Can duty cycle exceed 100%?
No. Duty cycle is bounded between 0% (always off) and 100% (always on). A pulse width that equals the full period gives 100% duty cycle. Any calculation that produces a value outside this range indicates an error in the input values (for example, a pulse width longer than the period).
Why do welders and compressors have a duty cycle rating?
These devices generate significant heat when operating and need rest periods to cool. A welder rated at 60% duty cycle at full current can safely arc for 6 minutes out of every 10-minute block. Exceeding the rated duty cycle does not trip a breaker immediately but causes cumulative thermal buildup that degrades insulation and shortens component life. The standard measurement window is 10 minutes for most power tools.
What is a safe injector duty cycle?
Most factory port fuel injectors are designed to operate reliably up to about 80-85% duty cycle. Beyond that threshold the injector may not fully close between pulses, fuel delivery becomes nonlinear, and the injector runs hotter. Performance tuners aim to keep injector duty cycle below 80% at maximum load, and under 70% is a comfortable margin for a street-driven vehicle.
How does PWM control average voltage?
A PWM signal rapidly switches between supply voltage and zero at a fixed frequency. Because the switching is much faster than the load can respond, the load sees the time-averaged voltage, which equals supply voltage multiplied by the duty cycle fraction. At 30% duty cycle with a 12 V supply the average voltage is 3.6 V; at 75% it is 9 V. This is how microcontrollers dim LEDs, control motor speed, and regulate power without lossy resistors.