- Published 29 Aug 2025
- Last Modified 29 Aug 2025
- 2 min
555 Timer Calculator
Use our free 555 timer calculator to find the figures you need easily and accurately.
Our handy 555 timer calculator can be used for either monostable 555 timer or astable 555 timer configurations. You can also select from various standard units of measurement for each input, giving you even more flexibility.
With 555 timer monostable mode, you merely need to add your figures into the interactive R1 resistor value and C1 capacitance fields before clicking the ‘calculate’ button to instantly generate the output pulse duration.
Conversely, in astable mode, there is an additional field where you can add the R2 resistor value, thus allowing the tool to provide the time high, time low, and frequency.
Understanding 555 Timer ICs
555 timer integrated circuits (ICs) are typically configured to produce a square waveform output. These common 555 timer IC circuits can be configured in either monostable or astable mode:
- Monostable mode: This configuration produces a short, single high pulse output, generated for a single input event (one-shot mode). The duration of this is determined by the circuit’s capacitance and resistance values
- Astable mode: This configuration produces a continuous square wave output (free-running mode). Both the high and low times and the frequency are determined by the circuit’s capacitance and resistance values.
555 Timer Calculations
The 555 timer calculator enables you to determine the output pulse frequency or duration based on the circuit’s capacitance and resistance values.
For monostable mode, the following 555 timer formula can be used:
T = 1.1RC
In other words, the output signal duration can be described as:
Time in Seconds (T) equal to the constant of 1.1, multiplied by the Resistance (R), multiplied by the Capacitance (C).
The following formulas can be used for astable mode:
Time high formula:
Tₕ = 0.693(R₁ + R₂)C
Time low formula:
Tₗ = 0.693R₂C
Frequency formula:
f = 1.44/((R₁ + 2R₂)C)
