555 Timer Calculator
Calculate the frequency, period, and duty cycle of a 555 timer IC in astable (oscillator) mode from R1, R2, and C values.
555 Timer Output
555 Timer in Astable Mode produces a continuous square wave.
Frequency = 1.44 / ((R1 + 2×R2) × C)
Duty Cycle = (R1 + R2) / (R1 + 2×R2) × 100%
Time HIGH (t1) = 0.693 × (R1 + R2) × C
Time LOW (t2) = 0.693 × R2 × C
Notes:
- R1 and R2 should be between 1 kΩ and 10 MΩ
- Standard duty cycle is always > 50 % in basic astable mode
- For 50 % duty cycle, add a diode across R2
- C is in Farads — enter in µF or nF and the calculator converts