555 Timer Calculator

How to use the 555 timer calculator

1. Choose astable (oscillator) or monostable (one pulse).
2. Enter R1, R2 for astable mode, and C.
3. See the frequency, high and low times and duty cycle, or the pulse length.

Frequently asked questions

What are the formulas?

Astable: high time = 0.693 × (R1 + R2) × C, low time = 0.693 × R2 × C. Monostable: pulse = 1.1 × R × C.

Why is the duty cycle always over 50%?

In the standard astable circuit the capacitor charges through R1 and R2 but discharges only through R2. Add a diode across R2 for duty cycles below 50%.