About this tool
555 Timer Calculator is a free, in-browser tool for the classic NE555 timer chip. It finds the astable output frequency and duty cycle from R1, R2 and C, or the monostable pulse width from R and C. All calculations happen locally in your browser.
In astable mode the frequency is f = 1.44 / ((R1 + 2·R2)·C), the period is T = 1/f, and the duty cycle is (R1 + R2) / (R1 + 2·R2) × 100%. The output is high for tHigh = 0.693·(R1 + R2)·C and low for tLow = 0.693·R2·C. In monostable (one-shot) mode a single trigger produces a pulse of width T = 1.1·R·C. Resistors accept Ω, kΩ or MΩ and the capacitor accepts µF, nF or pF via the unit selectors.
Use it to design a blinker, clock or one-shot: adjust the resistors and capacitor and watch frequency, duty cycle and timing update instantly. Note the standard 555 astable duty cycle is always above 50% because R1 is in the charge path but not the discharge path.