Capacitor Energy Calculator

Created by Wojciech Sas, PhD candidate
Reviewed by Bogna Szyk and Jack Bowater
Last updated: Nov 24, 2021

This is the capacitor energy calculator, a simple tool which helps you evaluate the amount of energy stored in a capacitor. You can also the find how much charge has accumulated in the condenser. Read on to learn what kind of energy is stored in a capacitor, and what is the equation of capacitor energy.

What is the energy stored in a capacitor?

A capacitor is an electronic component commonly used in circuits. Its function is to store an electrical charge. In standard parallel plate capacitors, charges of equal but opposite value are present on adjacent plates (for a spherical capacitor there are concentric spheres instead of plates). These charges create an electric field between them, made up of a certain amount of the circuit's of energy. Because we are talking about stored charges, this is an example of potential energy. However, in this case, you cannot use the standard potential energy formula.

Capacitor energy formula

How do you estimate the energy, E, stored in a capacitor with a capacitance, C, and an applied voltage, V? It's equivalent to the work done by a battery to move charge Q to the capacitor. The resulting equation is:

E = 1/2 * C * V².

Using the general formula for capacitance, C = Q / V, we can rewrite the capacity energy equation in two other analogous forms:

E = 1/2 * Q² / C or E = 1/2 * Q * V.

Electrical energy in a capacitor - an example

How much energy can be stored in a capacitor with capacity C = 300 μF, when we connect it to a voltage source of V = 20 V? Let's work it out together!

  • To make our life easier, use scientific notation for the capacitance: C = 3·10⁻⁴ F
  • Following the capacity energy formula, the outcome is evaluated as: E = 1/2 * 3·10⁻⁴ F * (20 V)² = 6·10⁻² J
  • The energy stored in the capacitor can also be written as 0.06 J or 60 mJ
  • Additionally, we can estimate the overall charge accumulated in the capacitor: Q = C * V = 3·10⁻⁴ F * 20 V = 6·10⁻³ C = 6 mC
  • ... or you can simply save your time by using this capacitor energy calculator, which does all the computations for you automatically!

By the way, if you have a system with more than one capacitor, you'd better check our capacitors in series or capacitors in parallel calculators to find the total capacitance quickly, because this is the value you should use in the formula for the capacitor's energy.

Energy transformations in an LC circuit

An LC circuit is a system that is composed of an inductor and a capacitor. In practice, it can be generalised as an RLC circuit due to some resistance in the system. Once the circuit processes the signal of a resonant frequency, the potential energy of the capacitor continuously transforms into the magnetic energy produced by a current flowing through the coil. These kinds of circuits are widely used in signal processing, or the sending and receiving of radio waves.

Wojciech Sas, PhD candidate
Capacity (C)
F
Voltage (V)
V
Stored charge (Q)
C
Stored energy (E)
J
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