RC Time Constant Calculator

Calculate RC time constants, charging/discharging curves, cutoff frequencies, and design RC filters for various electronic applications.

RC Circuit & Charging Curve

RC Circuit

    Vin ──┬─── R ───┬─── Vout
          │         │
          │         C
          │         │
          └─────────┴─── GND
          
    τ = R × C
    fc = 1/(2πRC)

Charging Curve

1τ
63.2%
3τ
95%
5τ
99.3%

Calculation Method

Resistance & Capacitance (τ = RC)

Ω
µF

About RC Time Constants

The RC time constant (τ = RC) determines how quickly a capacitor charges or discharges through a resistor. It's fundamental to timing circuits, filters, and signal processing.

Key Concepts:

  • 1τ (63.2%): Time to reach 63.2% of final value
  • 3τ (95%): Considered "fully charged" for practical purposes
  • 5τ (99.3%): Nearly complete charge/discharge
  • Cutoff Frequency: -3dB point in frequency response

Applications:

  • Timing: Delays, oscillators, pulse generators
  • Filtering: Low-pass, high-pass, band-pass filters
  • Coupling: AC coupling, DC blocking
  • Integration: Analog computers, signal processing

Design Guidelines:

  • For timing: Choose τ based on required delay
  • For filtering: Set fc = 1/(2πRC) at desired frequency
  • Consider component tolerances (±5% to ±20%)
  • Account for temperature effects on components