555 Timer Calculator

Calculate component values for astable and monostable circuits

Presets:
+Vcc 555 1 2 3 4 GND TRG OUT RST 8 7 6 5 VCC DIS THR CV R1 10kΩ R2 10kΩ C 10µF 10nF OUT
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Output Waveform

555 Timer Formulas

Astable Mode (Oscillator)

Produces a continuous square wave output.

Frequency = 1.44 / ((R1 + 2×R2) × C)
Time High = 0.693 × (R1 + R2) × C
Time Low = 0.693 × R2 × C
Duty Cycle = (R1 + R2) / (R1 + 2×R2)

Note: Standard astable circuits always have duty cycle > 50%. For 50% duty cycle, use a diode across R2 or use the 555 in different configuration.

Monostable Mode (One-Shot)

Produces a single pulse when triggered.

Pulse Width = 1.1 × R1 × C

Trigger the input with a falling edge (pull pin 2 low briefly). Output goes high for the calculated time, then returns low.