How this calculator works
A capacitor stores energy in its electric field. Charging it raises its voltage, so the last increment of charge requires more work than the first. Integrating that work produces the factor of one half. These equations assume constant capacitance and exclude leakage, series resistance and dielectric losses.
Formula
Q = C V; E = C V²/2 = Q V/2 = Q²/(2 C).
Worked example
A 2 F capacitor at 3 V holds 6 C of charge and 9 J of energy. Conversely, 12 J stored with 4 C implies 6 V and 0.6666667 F.
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Frequently asked questions
Can I enter a negative voltage?
This tool uses voltage and charge magnitudes; reversing polarity does not change energy. Follow the polarity rating of the actual component.
Is all stored energy delivered to a load?
No. Wiring, switching and series resistance dissipate energy, and a load may stop operating before the capacitor reaches zero volts.
Why does doubling voltage quadruple energy?
Energy depends on voltage squared. The capacitor voltage rating must still be respected.