555 Timer Calculator
Astable and monostable modes — enter R and C values to get frequency, period, duty cycle, or pulse width.
Frequency
68.7 Hz
Period
14.6 ms
Duty cycle
52.4%
High time
7.62 ms
Low time
6.93 ms
Frequently Asked Questions
What is astable mode?+
The 555 oscillates continuously between high and low, producing a square wave. Frequency = 1.44 / ((R1 + 2×R2) × C).
What is monostable mode?+
A single trigger produces one timed output pulse. Pulse width = 1.1 × R × C. Used for debouncing, time delays, and one-shot events.
What is duty cycle?+
The percentage of each period that the output is HIGH. In standard astable mode the duty cycle is always above 50% (R1 adds to the high time only).