This 555 timer calculator covers both astable (oscillator) and monostable (one-shot) modes. Enter your resistor and capacitor values above to get the frequency, duty cycle, or pulse width.
Formulas
Astable f = 1.44 ÷ ((R1 + 2R2) × C) Monostable pulse T = 1.1 × R × C
Example
Monostable, R = 10 kΩ, C = 10 µF: T = 1.1 × 10,000 × 10µF = 0.11 s.
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Frequently Asked Questions
How do I calculate 555 timer values?
For astable mode use f = 1.44 / ((R1 + 2R2) C); for monostable use pulse width T = 1.1 R C.
What is the difference between astable and monostable?
Astable oscillates continuously; monostable produces a single timed pulse when triggered.
What capacitor should I use?
Larger capacitors give lower frequencies or longer pulses; pick R and C together to hit your target timing.