555 Monostable Calculator
One-shot timer math — t = 1.1·R·C — pulse widths from microseconds to minutes, trigger rules, the retrigger gotcha and honest accuracy limits.
Preset: 100 kΩ + 10 µF → 1.1 s pulse. The trigger (pin 2, falling below ⅓ Vcc) must release before the pulse ends — AC-couple long button presses. Pulse width is supply-independent from 5–15 V.
555 Monostable Calculator computes the one-shot output pulse width of a 555 monostable from its timing resistor and capacitor — free, instant and private in your browser. Circuit designers needing fixed delays, debouncing and pulse stretching without code use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About 555 Monostable Calculator
555 Monostable Calculator computes the one-shot output pulse width of a 555 monostable from its timing resistor and capacitor using the standard engineering relation: t = 1.1·R·C — the 1.1 is ln(3), the time an RC needs to charge from 0 to the ⅔·Vcc threshold. Worked live: 100 kΩ + 10 µF → a clean 1.1 s pulse: the staircase-light timer, the debouncer, the hold-this-relay-a-second block. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use 555 Monostable Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use 555 Monostable Calculator?
- ✓Implements the real formula — t = 1.1·R·C — the 1.1 is ln(3), the time an RC needs to charge from 0 to the ⅔·Vcc threshold — with the substitution shown, not a black box
- ✓Built for circuit designers needing fixed delays, debouncing and pulse stretching without code
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate 555 monostable?+
The one-shot output pulse width of a 555 monostable from its timing resistor and capacitor follows t = 1.1·R·C — the 1.1 is ln(3), the time an RC needs to charge from 0 to the ⅔·Vcc threshold. For example, 100 kΩ + 10 µF → a clean 1.1 s pulse: the staircase-light timer, the debouncer, the hold-this-relay-a-second block. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Why does my 555 one-shot output stay high forever?+
The trigger is still active: pin 2 is level-sensitive, and held below ⅓ Vcc past the timeout it overrides the timing and pins the output high. AC-couple the button — 10 nF from switch to pin 2 with a 10 kΩ pull-up — so the chip sees a brief edge regardless of how long the finger stays down.
Can I restart the timing period with a new trigger (retrigger)?+
Not with a standard 555 — triggers during the interval are ignored and the pulse completes on schedule. Great for debouncing, wrong for motion-sensor lights where each detection should restart the countdown. For retriggerable one-shots use a 74HC123/4538, or pulse pin 4 (reset) low then re-trigger.
Is the 555 Monostable Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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