Calculates the electrical energy stored in a charged capacitor.
How it works
Half the capacitance is multiplied by the square of the voltage across the capacitor.
What this does not include
This does not include the energy stored in an inductor’s magnetic field — for that, use this site’s inductor energy calculator instead, which uses a different formula for a different kind of energy storage.
How to use this calculator
- Enter the capacitance and the voltage across the capacitor.
A worked example
A 0.001 F capacitor charged to 12 V: energy = ½CV² = 0.5 × 0.001 × 12² = 0.072 J.
A 0.0001 F capacitor charged to 100 V: energy = 0.5 J — a much smaller capacitance but a far higher voltage stores more total energy, since energy scales with the square of voltage.
What the variables mean
| Variable | Meaning |
|---|---|
| Capacitance | The capacitor’s charge storage capacity, in farads |
| Voltage | Voltage across the capacitor |
Edge cases worth knowing
Stored energy scales with the square of voltage, not linearly. Doubling the voltage quadruples the stored energy — the same squared relationship seen in Coulomb’s law and kinetic energy.
A negative capacitance has no physical meaning — capacitance is always a positive quantity, so the calculator declines to show a result for a negative input.
Frequently asked questions
Why is voltage squared in this formula?
Energy grows with the square of voltage because both the stored charge and the voltage driving it scale together — doubling voltage quadruples stored energy.
What’s a real-world use for capacitor energy storage?
Camera flashes, power-supply smoothing, and energy-recovery systems all rely on capacitors’ ability to store and quickly release electrical energy.
Does capacitor energy discharge instantly?
No — the discharge rate depends on the circuit’s resistance, described by the RC time constant, which this calculator doesn’t cover directly.
