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NE555 Astable Calculator.

Calculate ideal 555 astable oscillator frequency and duty cycle.

On-device calculationNo signup
01

Set your values

Results update as you type.

Frequency: 68.571429 Hz

Frequency

0.000000Hz
Period: 0.014583 s

Period

0.000000s
Duty cycle: 52.380952 %

Duty cycle

0.000000%

Results update automatically as you type.

Use Cases

Designing an LED flasher circuit

Quickly determine the resistor and capacitor values needed to achieve a desired flash rate for an LED flasher using a 555 timer in astable mode.

Example: Set R1=1kΩ, R2=10kΩ, C=10µF to get a frequency of about 1.2 Hz.

Generating a clock signal for digital circuits

Calculate the frequency and duty cycle of a 555 astable oscillator to use as a clock source for timers, counters, or other digital logic.

Example: For a 1 kHz clock, try R1=1kΩ, R2=6.8kΩ, C=0.1µF.

Frequently Asked Questions

How does the NE555 astable calculator work?
The calculator uses the standard formulas for a 555 timer in astable mode: frequency = 1.44 / ((R1 + 2*R2) * C) and duty cycle = (R1 + R2) / (R1 + 2*R2) * 100%. You input R1, R2, and the timing capacitance, and it computes the output frequency and duty cycle.
What is the duty cycle in a 555 astable circuit?
Duty cycle is the percentage of time the output is high during one cycle. In the standard astable configuration, the output is high while charging through R1 and R2, and low while discharging through R2 only. The formula used is (R1 + R2) / (R1 + 2*R2) * 100%.
Can I use this calculator for any 555 timer IC?
Yes, the formulas apply to all standard 555 timer ICs (e.g., NE555, LM555, etc.) when used in astable mode. The calculator assumes ideal conditions, so real-world results may vary slightly due to component tolerances and temperature.

Tips & Common Mistakes

Tips

  • Ensure all values are in the correct units: R1 and R2 in ohms (Ω), capacitance in farads (F). Use scientific notation for small capacitances (e.g., 1e-6 for 1µF).
  • For a duty cycle close to 50%, choose R1 much smaller than R2. However, note that the standard astable circuit cannot achieve exactly 50% duty cycle.
  • Use standard resistor and capacitor values (e.g., E12 series) to make it easier to source components.

Common Mistakes to Avoid

  • Forgetting to convert units: using microfarads (µF) instead of farads (F) without converting to 1e-6 F, leading to incorrect results.
  • Using the wrong formula: mixing up the frequency and duty cycle formulas, or using the monostable formula instead of the astable one.
  • Assuming the duty cycle can be set to exactly 50% with any resistor values; the standard astable configuration always has a duty cycle greater than 50%.

Last updated: August 13, 2026