The 555 Timer Monostable Calculator computes the output pulse duration for a 555 timer circuit wired in monostable mode — where a single trigger produces one timed output pulse. Enter your Resistance (R) and Capacitance (C) values (with units) to get the Output Pulse Width (T) in seconds and milliseconds, plus the Equivalent Frequency of that pulse.
Output Pulse Width (T)
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Output Pulse Width
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Equivalent Frequency
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A 555 timer monostable circuit is a one-shot timer that produces a single output pulse of fixed duration when triggered. The output goes high for a predetermined time period and then returns to low, making it useful for timing applications.
The output pulse width is calculated using the formula T = 1.1 × R × C, where T is the pulse width in seconds, R is the resistance in ohms, and C is the capacitance in farads.
Only the external resistor (R) and capacitor (C) determine the output pulse width. The 1.1 factor comes from the internal voltage divider and charging characteristics of the 555 timer IC.
Typical resistance values range from 1kΩ to 1MΩ, while capacitance values typically range from 1nF to 1000μF. The combination determines the output pulse duration from microseconds to several minutes.
A 555 monostable circuit is triggered by a negative-going pulse (falling edge) applied to pin 2 (trigger input). The trigger pulse should be shorter than the desired output pulse width.
For timing applications, use stable capacitors like ceramic, polyester, or tantalum types. Avoid electrolytic capacitors for precision timing as they have poor stability and high leakage current.
Monostable produces a single output pulse when triggered (one-shot), while astable continuously oscillates producing a square wave output without requiring an external trigger.
Common applications include time delays, pulse width generation, switch debouncing, timeout circuits, and sequential timing in digital systems. They're widely used in automation and control systems.