RC time constant: 1kΩ × 1nF = 1.0 µs (fc ≈ 159.15 kHz)
Worked answer for a first-order RC network of 1kΩ and 1nF: time constant, cutoff frequency and settling time.
Time constant τ 1.0 µs fc ≈ 159.15 kHz · settles in 5.0 µs (5τ)
| Resistor (R) | 1kΩ |
| Capacitor (C) | 1nF |
| Time constant τ = R · C | 1.0 µs |
| Cutoff frequency fc = 1 / (2π·R·C) | 159.15 kHz |
| Settling time (5τ, ≈99.3%) | 5.0 µs |
| Elapsed time | Multiple of τ | Charge |
|---|---|---|
| 1.0 µs | 1τ | 63.2% |
| 2.0 µs | 2τ | 86.5% |
| 3.0 µs | 3τ | 95% |
| 4.0 µs | 4τ | 98.2% |
| 5.0 µs | 5τ | 99.3% |
A charging capacitor reaches 63.2% of the final voltage after one time constant (1.0 µs) and is considered fully charged (≈99.3%) after five — here 5.0 µs.
Different values? Enter any R and C in the interactive tool:
Open the RC Time Constant Calculator →Disclaimer: These figures assume an ideal first-order RC network. Real resistors and capacitors carry tolerances, and capacitors have ESR and voltage/temperature dependence, so the measured time constant will differ. Confirm against your parts' datasheets.