Capacitor Charge Calculator
Find charge, energy, time constant and the charging voltage of an RC circuit.
Results update as you type.
About this calculator
A capacitor stores charge Q = C × V and energy E = ½ × C × V². When charged through a resistor it follows V(t) = V × (1 − e^(−t/τ)) with time constant τ = R × C. Enter the supply voltage, capacitance, series resistance and a time to see the state of the circuit.
Frequently asked questions
What is the time constant of an RC circuit?
The time constant τ = R × C is the time to charge to about 63% of the supply voltage. After 5τ the capacitor is regarded as fully charged (>99%).
How much energy does a capacitor store?
Energy is E = ½ × C × V². A 1000 µF capacitor at 5 V stores ½ × 0.001 × 25 = 0.0125 joules.
What is the difference between charging and discharging?
Charging rises toward the supply as V(1 − e^(−t/τ)); discharging falls from the starting voltage as V·e^(−t/τ). Both reach ~99% of the change after 5 time constants.
Results are estimates for general guidance only, not financial, medical or tax advice.