Capacitor Energy Calculator

Work out capacitor energy instantly with clear inputs, formula shown and shareable results.

About Capacitor Energy Calculator

Stored energy is half C V squared, so it rises with the square of voltage: doubling the charge voltage quadruples the energy. That is why a charged high-voltage capacitor is dangerous long after the supply is off, and why pulse applications favour voltage over capacitance.

Formula

Capacitor energy

E = 0.5 x C x V^2; Q = C x V

Worked example

With the default values below, Capacitor Energy Calculator returns Energy stored of 9.33. Change any input above and every figure here is recalculated in your browser.

Inputs used

Capacitance: 4,700 µF
Charged voltage: 63 V
Discharge duration: 0.05 s

Results

Energy stored: 9.33 J
Charge stored: 296.10 mC
Average power over the discharge: 186.54 W
Energy stored: 0.002591 Wh

Step by step

1Values used
2Capacitor energy
3Energy stored= 9.33 J
4Charge stored= 296.10 mC
5Average power over the discharge= 186.54 W
6Energy stored= 0.002591 Wh

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 6 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Why is energy only half QV?

Because voltage rises linearly as charge accumulates, so the average voltage during charging is half the final value.

How long does a capacitor stay dangerous?

Until it is deliberately discharged. With megohm-level leakage a large capacitor can hold a lethal charge for hours, which is why bleeder resistors are fitted.