Capacitor Charge & Energy Calculator

The formulas

A capacitor of capacitance C charged to voltage V holds a charge:

Q = C · V

and stores energy:

E = ½ · C · V²

Where:

• C is capacitance in farads (F). Microfarads convert with 1 µF = 0.000001 F.
• V is voltage in volts (V).
• Q is charge in coulombs (C).
• E is energy in joules (J).

Because energy depends on the square of the voltage, doubling the voltage quadruples the stored energy — while only doubling the charge.

Worked example

Take a 100 µF capacitor charged to 12 V.

• C = 100 µF = 0.0001 F
• Q = C · V = 0.0001 × 12 = 0.0012 C = 1.2 mC
• E = ½ · C · V² = 0.5 × 0.0001 × 12² = 0.5 × 0.0001 × 144 = 0.0072 J = 7.2 mJ

So this capacitor holds 1.2 mC of charge and 7.2 mJ of energy.

Quick reference

Pitfalls to avoid

• Watch the units. Capacitance is almost always printed in µF, nF or pF — convert to farads before doing math by hand. The calculator assumes the input is in µF.
• Respect the voltage rating. Never charge a capacitor above its rated voltage; the energy that makes it useful is also the energy that makes a failure violent.
• Large banks bite. A big, high-voltage capacitor can hold a dangerous charge long after power is removed. Always discharge through a resistor before handling.
• Energy ≠ charge. They scale differently with voltage — Q is linear, E is quadratic. Confusing the two is the classic mistake.