RC Time Constant Calculator
RC Time Constant & Filtering
The time constant τ (tau) determines how fast an RC circuit charges/discharges. At 5τ, the capacitor is 99.3% charged. Use this for debouncing switches, low-pass filtering, power-on delays, and audio filter design. Also calculates the -3dB cutoff frequency for AC circuits.
Charging curve shows voltage rise to 63% at τ and 99% at 5τ
10 000 Ω = 10 kΩ
Common RC values
Debounce: 10 kΩ + 100 nF = 1 ms
Audio LPF: 10 kΩ + 1 μF = 15.9 Hz
RF decoupling: 100 Ω + 100 pF = 15.9 MHz
Time Constant τ
1.00 ms
- Charge to 63.2% (1τ)
- 1.00 ms
- Charge to 86.5% (2τ)
- 2.00 ms
- Full charge ≈ 99% (5τ)
- 5.00 ms
- -3 dB cutoff frequency
- 159.15 Hz
τ = R × C · fc = 1 / (2π × R × C)
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