Capacitor Charge and Energy Calculator
Calculate the charge stored on a capacitor and its stored energy from capacitance and voltage.
How it works
Q = C · V and E = ½ · C · V²
A capacitor stores electric charge in proportion to the voltage across it, with the capacitance as the constant of proportionality. Capacitance is entered in microfarads and converted to farads (divide by one million) so the charge comes out in coulombs. The energy stored grows with the square of the voltage.
Worked example
A 100 µF capacitor at 12 V holds Q = 0.0001 F × 12 = 0.0012 C (1,200 µC) and stores E = ½ × 0.0001 × 12² = 0.0072 J.
Frequently asked questions
Why convert microfarads to farads?
The farad is the SI unit, so Q = C·V gives coulombs only when C is in farads. One microfarad is one millionth of a farad, so the calculator divides your input by 1,000,000.
Why does energy depend on voltage squared?
As charge builds up, the voltage rises, so later charge is added at higher voltage. Integrating over the charging process gives ½·C·V², not C·V².
What is a coulomb?
A coulomb (C) is the SI unit of electric charge, equal to the charge moved by one ampere in one second. Capacitor charges are often small, so results are also shown in microcoulombs.
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Educational estimate. Check the formula and units for your exact case.