Capacitor Energy Calculator
Enter a capacitance and a voltage to get the energy stored in a capacitor in joules — and see why that energy climbs with the square of the voltage.
What is capacitor energy?
The energy held in the field
A charged capacitor stores energy in the electric field between its plates. The energy was supplied while the capacitor was being charged, and it can be released again — sometimes in a fraction of a second — when the capacitor discharges. The capacitor energy calculator turns two measurements, the capacitance in farads and the voltage in volts, into the stored energy in joules. It is the number behind camera flashes, defibrillators, and the smoothing capacitors in a power supply.
Enter a capacitance in farads and a voltage in volts to get the stored energy in joules instantly.
The energy stored in a capacitor is half the capacitance multiplied by the voltage squared.
E = ½ × C × V²The voltage is squared, so it dominates the result: a small change in voltage produces a large change in stored energy. The capacitance enters to the first power, so it raises the energy more gently. Use farads and volts and the energy comes back in joules.
Suppose a 1000 µF capacitor (0.001 F) is charged to 10 V.
Square the voltage
10² = 100 — the squared voltage that drives the energy.
Multiply by the capacitance
0.001 × 100 = 0.1 — capacitance times voltage squared.
Take half
½ × 0.1 = 0.05 J — the energy stored in the capacitor.
The stored energy (0.05 J for the capacitor above) is how much work the capacitor can do when it discharges — the energy a flash tube, a motor, or a spark must absorb. The crucial insight is that this energy scales with the square of the voltage: double the voltage from 10 to 20 V and the stored energy jumps fourfold, from 0.05 to 0.2 J, while the capacitance only changes things in direct proportion. A bigger capacitance stores more energy at the same voltage, but doubling the capacitance only doubles the energy — voltage is the lever that moves the result the most. This is exactly why a charged capacitor can deliver a sudden, sharp jolt even at a modest voltage: a large capacitance bank releases its whole charge almost instantly, so even tens of volts can sting or damage components. It is also why you should treat any charged capacitor with respect and discharge it safely before handling.
The formula is exact, but a couple of practical points are worth keeping in mind.
Consistent units and ideal capacitors
This calculator gives the energy stored in an ideal capacitor and assumes the full voltage is applied. Keep your units consistent — farads for capacitance and volts for voltage — or the joules will be wrong: convert microfarads to farads by dividing by one million, and nanofarads by dividing by one billion, before you enter the value. Real capacitors also have a maximum rated voltage; exceeding it can destroy the component.