Case 1
- Timing resistor R (Ω)
- 10000Ω
- Timing capacitor C (µF)
- 10µF
0.110000s
Open with these valuesNE555 Monostable Calculator
0.110000s
Result: 0.110000 sOne trigger, one pulse of fixed length, however long the trigger itself lasted. The width is T = 1.1 × R × C: 10 kΩ with 10 µF gives 0.11 s. The 1.1 is ln(3) rounded, because the capacitor starts at zero and runs to two thirds of the supply — the astable circuit uses ln(2) instead.
The numbers at a glance
Held fixed: Timing resistor R (Ω) 10,000.000 Ω.
| Timing capacitor C (µF) (µF) | Result (s) |
|---|---|
| 2.500000 | 0.027500 |
| 5.000000 | 0.055000 |
| 7.500000 | 0.082500 |
| 10.000000Your value | 0.110000 |
| 12.500000 | 0.137500 |
| 15.000000 | 0.165000 |
| 17.500000 | 0.192500 |
| 20.000000 | 0.220000 |
Worked examples
Case 2
- Timing resistor R (Ω)
- 47000Ω
- Timing capacitor C (µF)
- 1µF
0.051700s
Open with these valuesCase 3
- Timing resistor R (Ω)
- 1000Ω
- Timing capacitor C (µF)
- 0.1µF
0.000110s
Open with these valuesHow it's calculated
T = 1.1 × R × C
- StepEnter the timing resistor in ohms — 47 kΩ is 47000.
- StepEnter the timing capacitor in microfarads — 100 nF is 0.1.
- ResultRead the pulse width in seconds; multiply by 1000 for milliseconds.
Reference table
| R (Ω), C (µF) | Same pulse in ms | Pulse width (s) |
|---|---|---|
| 1000, 0.1 | 0.11 ms | 0.000110 |
| 4700, 0.47 | 2.43 ms | 0.002430 |
| 47000, 1 | 51.7 ms | 0.051700 |
| 10000, 10 | 110 ms | 0.110000 |
| 220000, 2.2 | 532.4 ms | 0.532400 |
| 100000, 10 | 1100 ms | 1.100000 |
Questions
How do I calculate the pulse width of a 555 monostable circuit?
Use T = 1.1 × R × C, with R in ohms and C in farads. For R = 10 kΩ and C = 10 µF that is 0.11 s, or 110 ms. Enter the capacitance in microfarads here and the conversion is done for you.
Why is the constant 1.1 and not 0.693?
Because the voltage swing is different. In one-shot mode the capacitor starts at zero and charges until it reaches two thirds of the supply, which takes ln(3) time constants; the free-running astable circuit only swings between one third and two thirds, which is ln(2). Same chip, different starting point.
Is 1.1 an exact constant?
No — ln(3) is 1.098612, and 1.1 is the two-digit form that datasheets and textbooks print. The difference is about 0.13 %, far smaller than the tolerance of any real resistor or electrolytic capacitor. This calculator keeps 1.1 so its numbers match published 555 tables.
What is monostable (one-shot) mode?
The output rests low until a trigger arrives, then goes high for a fixed time and falls back. One trigger produces one timed pulse, no matter how long the trigger itself lasted. It is used for timed lights, button debouncers and turning a momentary press into a fixed delay.
How do I make the pulse longer or shorter?
The width is linear in both R and C, so raising either value lengthens the pulse. A 10 µF capacitor with 100 kΩ gives 1.1 s; the same capacitor with 1 kΩ gives 11 ms. A trimmer for R lets you dial the timing in.
Sources and last check
Information, not professional advice.