Capacitor Charge Calculator

About the RC Time Constant

When a capacitor charges through a resistor, the voltage does not rise instantly — it follows an exponential curve governed by the RC time constant Ï„ (tau). The formula is simple: τ = R × C, where R is the resistance in ohms and C is the capacitance in farads. After one time constant, the capacitor reaches approximately 63.2% of the supply voltage. After five time constants it is considered fully charged (≈ 99.3%).

Charge and Discharge Equations

• Charging: Vc(t) = Vs × (1 − e^(−t/τ))
• Discharging: Vd(t) = Vs × e^(−t/τ)

The tool computes the capacitor voltage and discharge voltage at each multiple of Ï„ from 1Ï„ to 5Ï„. This is useful when designing RC filters, timing circuits, debounce networks, and power supply smoothing capacitors.

Practical Applications

RC time constants appear throughout electronics: in passive low-pass and high-pass filters (cutoff frequency f = 1/(2Ï€RC)), in 555 timer circuits to set pulse width, in ADC sample-and-hold circuits, and in power supply bulk capacitance calculations. The calculator supports resistances from ohms to megaohms and capacitances from farads down to picofarads, covering everything from audio filters to high-speed digital circuits.