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555 Timer Astable Calculator

Find frequency, high time, low time and duty cycle for the standard two-resistor 555 oscillator.

Ideal component relationshipsUnits and assumptions explained below
555 timer workbench
555 timer workbench

Enter RA, RB and C for the standard astable connection.

See the method

Set the timing components

Runs on your device

Frequency and pulse timing

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter resistor ra, resistor rb, capacitance.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

High time = ln(2)(RA+RB)C; low time = ln(2)RB C; frequency = 1/(high + low). Convert kΩ and µF to SI first.

A WORKED EXAMPLE

Using resistor ra = 10 kΩ, resistor rb = 10 kΩ, capacitance = 10 µF, the result is 4.80898347 Hz. Change these example inputs to match your task; use the method above to check each step.

Understanding your result

Standard astable connection without steering diodes. Component tolerance and device limits affect actual timing; the duty cycle is above 50%.

What to keep in mind

Standard astable connection without steering diodes. Component tolerance and device limits affect actual timing; the duty cycle is above 50%. Ideal-component calculation for study and estimation. It does not select safe wiring, protective devices or component ratings for an installation.

Common questions

How do I use this 555 timer astable calculator?

Find frequency, high time, low time and duty cycle for the standard two-resistor 555 oscillator. Enter resistor ra in kΩ, resistor rb in kΩ, capacitance in µF. The starting example is editable; use values for the same system or project.

Which assumptions affect this result?

Standard astable connection without steering diodes. Component tolerance and device limits affect actual timing; the duty cycle is above 50%.

Methodology maintained by ClarityKit. How these tools are built and checked.