Capacitor Charge Time Calculator

When you apply a voltage to an RC circuit, the capacitor doesn't charge instantly. Current flows through the resistor and gradually builds up charge on the capacitor plates. The rate of charging follows an exponential curve, getting slower as the capacitor voltage approaches the supply voltage.

The time constant τ = R × C tells you how fast the circuit responds. A 10kΩ resistor with a 100µF capacitor gives τ = 1s. After one time constant the capacitor is at 63.2% of Vcc. After five time constants it's at 99.3%, which is close enough to call it fully charged for most purposes.

One practical note: the capacitor voltage at any moment is V(t) = Vcc × (1 − e^(−t/τ)). If you need to reach a specific voltage, use the target voltage field above. This is useful when designing timing circuits, power supply filters, or debounce circuits where you need to hit a threshold voltage at a precise time.

Charging Reference

• 1τ: 63.2% of Vcc
• 2τ: 86.5% of Vcc
• 3τ: 95.0% of Vcc — practical threshold
• 5τ: 99.3% of Vcc — considered fully charged

Applications

• RC delay and timing circuits
• Power-on reset circuits
• Signal debouncing
• Analog filter design
• Flash charging circuits