Capacitor Energy Calculator

The energy stored in a capacitor is the potential energy held in the electric field between its plates. When a voltage is applied, opposite charges accumulate on the two plates, creating an electric field that stores energy. This energy can be released when the capacitor discharges through a circuit.

A capacitor stores energy by accumulating electric charge on its plates when connected to a voltage source. The separated positive and negative charges on opposite plates create an electric field between them, and the energy is stored in that field as electrical potential energy. The capacitor releases this energy when it discharges.

Use the formula E = ½ × C × V², where E is the energy in joules, C is the capacitance in farads, and V is the voltage in volts. You can also express it as E = Q²/(2C) or E = ½QV, where Q is the charge on the plates. All three forms are equivalent and give the same result.

Using the formula E = ½CV², convert 120 pF to 120 × 10⁻¹² F, then calculate: E = 0.5 × 120 × 10⁻¹² × (1.5)² = 1.35 × 10⁻¹⁰ J, or 0.135 nanojoules. You can verify this by entering the values directly into this calculator.

The factor of ½ arises because charging a capacitor is not done at constant voltage — the voltage across it builds up gradually from 0 to V as charge accumulates. The average voltage during charging is V/2, so the total energy delivered is ½QV = ½CV². This is why only half the energy supplied by the source ends up stored in the capacitor.

Capacitor energy is measured in joules (J) in the SI system. For small capacitors typically used in electronics, the stored energy is often in the range of microjoules (μJ) or millijoules (mJ). Capacitance is measured in farads (F), though practical capacitors are usually rated in picofarads (pF), nanofarads (nF), or microfarads (μF).

The charge Q on a capacitor's plates is given by Q = C × V, where C is capacitance and V is voltage. The stored energy relates to charge as E = Q²/(2C) or E = ½QV. Increasing either the capacitance or the voltage increases the stored charge, but energy grows with the square of voltage, making voltage the more powerful factor.

In an LC circuit (inductor-capacitor), energy oscillates between the capacitor's electric field and the inductor's magnetic field. When the capacitor is fully charged, all energy is stored electrically. As it discharges through the inductor, energy transfers to the magnetic field. This cycle repeats at the circuit's natural resonant frequency, f = 1/(2π√(LC)).