Capacitor Energy Calculator
Find the energy stored in a capacitor and the charge it holds from its capacitance and the voltage across it.
How it works
E = ½·C·V² · Charge Q = C·V (C in farads, V in volts, E in joules)
A charged capacitor stores energy in the electric field between its plates, given by E = ½·C·V². Because the voltage term is squared, the stored energy quadruples when you double the voltage but only doubles when you double the capacitance — so voltage rating matters enormously for energy storage. The charge held is Q = C·V. Capacitors release this energy very quickly, which is why they power camera flashes and defibrillators.
Worked example
A 1000 µF capacitor (0.001 F) charged to 12 V: energy = ½ × 0.001 × 12² = ½ × 0.001 × 144 = 0.072 J (72 mJ). The charge is Q = 0.001 × 12 = 0.012 C = 12 mC.
Sources: Capacitor — Wikipedia
Frequently asked questions
Why is the voltage squared in the energy formula?
As a capacitor charges, both the charge and the voltage build up together, so the average voltage during charging is half the final value. Integrating the work done gives E = ½·C·V², which is why raising the voltage has a much bigger effect on energy than raising the capacitance.
How is stored charge different from stored energy?
Charge Q = C·V (in coulombs) is how much electric charge sits on the plates, and it scales linearly with voltage. Energy E = ½·C·V² (in joules) is the work stored in the field and scales with the square of voltage — two different quantities with different units.
What is a microfarad?
A microfarad (µF) is one millionth of a farad. Everyday capacitors are usually rated in µF, nF or pF because a full farad is an enormous capacitance. This calculator converts your µF value to farads internally before applying the formula.
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This calculator is for educational purposes. Double-check important results before acting on them.