555 Timer Calculator – Free Online 555 timer calculator

Calculate frequency, duty cycle and pulse width for a 555 timer in astable or monostable mode.

f = 1 / (ln 2 × (R1 + 2 R2) × C) ≈ 1.44 / ((R1 + 2 R2) × C). Duty cycle is always above 50 % without a diode across R2.

Frequency	6.87 Hz
Period	145.561 ms
High time	76.246 ms
Low time	69.315 ms
Duty cycle	52.4 %

About this 555 timer calculator

Calculate the output of an NE555 timer. In astable mode get frequency, period, high and low time and duty cycle from R1, R2 and C; in monostable mode get the pulse width from R and C.

How to use the 555 Timer Calculator

Choose astable or monostable mode.
Enter the resistor and capacitor values.
Read the frequency, duty cycle or pulse width.

Example

R1 1 kΩ, R2 10 kΩ, C 10 µF  →  6.87 Hz, 52.4 % duty

Frequently asked questions

How do I get a duty cycle below 50 %?

Put a diode across R2 so the capacitor charges only through R1, or use a CMOS 555 in a different configuration.

Is my data safe?

Yes. The tool runs entirely in your browser using WebAssembly. Nothing you type or upload is sent to a server, logged or stored.

Is it free?

Yes, completely free with no sign-up, no limits and no watermarks. It also works offline once the page has loaded.