Free tool

555 Timer Calculator

Size an NE555 circuit from a much clearer interface. Choose monostable or astable mode and get the theoretical time or frequency from R and C.

Tools

Calculate timing and frequency for an NE555 circuit

The tool lets you move from R and C values to the expected timer behaviour. In monostable mode you get the pulse time; in astable mode, the frequency, period and duty cycle.

555 Timer Calculator

Select the operating mode of the IC and enter the resistors and capacitance with their units to get the expected result.

Introduce los valores requeridos para el modo seleccionado y usa unidades validas.
Result--The theoretical time or frequency of the timer will be shown according to the selected mode.

How to interpret each mode

The 555 is still a very useful reference for simple timing, one-shot triggering and basic oscillators.

Monostable
  • Genera un pulso unico tras un disparo.
  • Tiempo teorico: T = 1.1 x R1 x C
Astable
  • Oscila de forma continua con una frecuencia determinada por R1, R2 y C.
  • Permite estimar frecuencia, periodo y ciclo de trabajo.

Quick guide

What to check when using an NE555 in a real design

The 555 formulas help you size a design quickly, but in a real board, tolerances, capacitor leakage, temperature and IC limits also matter. Use the calculator as a starting reference and then verify the result on a prototype.

Lectura rapida

  • Monostable: un solo pulso tras el disparo.
  • Astable: oscilacion continua mientras haya alimentacion.
  • R y C condicionan directamente tiempo, frecuencia y duty cycle.
  • Capacitancias altas y resistencias muy grandes suelen introducir desviaciones practicas.

Monostable

Calcula el ancho del pulso teorico disparado por el circuito.

T = 1.1 x R1 x C

Astable

The period depends on the charge and discharge path through R1 and R2.

T = 0.693 x (R1 + 2R2) x C

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FAQ

Frequently asked questions

A short reference for the usual questions when sizing a circuit built around a 555 timer.

Which modes does the calculator cover?

It includes monostable and astable mode, which are the two most common NE555 configurations.

What does it return in monostable mode?

It returns the theoretical pulse time generated from R1 and C.

What does it return in astable mode?

It calculates frequency, period, high time, low time and duty cycle from R1, R2 and C.

Is the calculator free?

Yes. You can use it online without downloading anything.

Next step

Need help with the electronic design of your project?

If you are developing a product and need support with electronics, PCBs, firmware or technical validation, we can review your case and point you in the right direction.

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