RC Time Constant

Results

The RC time constant (τ = tau) defines how fast a capacitor charges or discharges through a resistor. After one time constant (1τ), the capacitor reaches 63.2% of the supply voltage during charging. After five time constants (5τ), it reaches 99.3% and is considered fully charged. This is fundamental to filter design, timing circuits, and signal processing.

τ = R × C · Full Charge ≈ 5 × τ · V(t) = Vs × (1 − e−t/τ)

Results

How to use this calculator

Step-by-Step Instructions

1. **Enter resistance in Ohms** The resistor through which the capacitor charges or discharges.
2. **Enter capacitance in µF** The capacitor value. Convert nF to µF by dividing by 1000 if needed.
3. **Click Calculate** Results show the time constant (τ) and the voltage at 1τ through 5τ intervals.

Worked Example

R = 10kΩ (10000Ω), C = 100µF τ = 10000 × 0.0001 = **1.0 second**

Full charge time (5τ) = **5.0 seconds**