555 Timer Calculator
Calculate astable frequency, duty cycle, charge and discharge time, or monostable pulse width for a 555 timer.
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About this tool
A 555 timer is either a free-running oscillator or a single pulse. This page solves frequency, duty cycle, charge and discharge time, or monostable pulse width from the resistors and capacitor you enter.
Use it when you are choosing parts for a blinker, a debounce pulse or a simple clock, before you solder. The report uses the standard timing formulas with your numbers.
Those formulas ignore the discharge transistor’s saturation voltage, capacitor tolerance, and the difference between bipolar and CMOS 555 parts. Measure the built circuit; do not treat the number as a finished design.
Example. Astable mode with RA 1 kΩ, RB 1 kΩ and C 1 µF reports a 1.386 ms charge, a 693 µs discharge, 481.00048100048 Hz and a 66.67% duty cycle.
Limit. The astable duty cycle is (RA+RB)/(RA+2×RB), so it stays above 50%, and the formula ignores discharge-transistor saturation.