Capacitor Energy Calculator
Calculate the energy stored in a capacitor and its charge from capacitance and voltage.
How it works
A charged capacitor holds energy in the electric field between its plates. The amount is E = ½ × C × V², where C is capacitance in farads and V is the voltage across it.
Because voltage is squared, it dominates the result. A 100 µF cap at 12 volts stores half of 0.0001 farads times 144, which comes to 0.0072 joules — but double the voltage and the energy quadruples.
The tool also reports charge, Q = C × V, the total charge sitting on the plates in coulombs. That's the figure that matters when you're timing a discharge or sizing a capacitor to hold up a supply through a brief dropout.
Frequently asked questions
Why is the energy in a small capacitor so tiny?
Ordinary microfarad-scale capacitors store fractions of a joule at everyday voltages. It takes big electrolytics or supercapacitors — thousands of microfarads or more — before the stored energy becomes something you'd feel.
Is a charged capacitor dangerous?
Small ones usually aren't, but high-voltage capacitors in power supplies and camera flashes can hold a painful or dangerous charge long after the power is off. Always discharge them safely before handling.
What's the difference between energy and charge?
Charge (Q = C·V) is how much electric charge is stored; energy (½CV²) is the work that charge can do. Two capacitors can hold the same charge but very different energy if their voltages differ.