19.2.2—W = 1/2 QV = 1/2 CV 2

For a linear capacitor, stored energy W=½QV=½CV²=Q²/(2C). The half factor comes from the average voltage during charging.

Choose the form matching known Q, V or C and keep units in farads, volts and coulombs.

A 100 μF capacitor at 20 V stores 0.020 J.

Using QV without the half factor doubles the energy for a capacitor charged from zero.