# [Capacitor Energy Calculator](https://blog.hirnschall.net/tools/capacitor-stored-energy/)

author: [Sebastian Hirnschall](https://blog.hirnschall.net/about/)

meta description: Calculate the energy stored in a capacitor. Solve for energy, capacitance, or voltage given the other two. Stored charge shown as additional output.

meta title: Capacitor Energy Calculator — Solve for E, C, or V

date published: 01.04.2025 (DD.MM.YYYY format)
date last modified: 22.04.2025 (DD.MM.YYYY format)

---

Calculator
----------

This calculator can solve for energy \( E \), capacitance \( C \), or voltage \( V \) when you provide the other two. The stored charge \( Q \) is always shown as an additional output.

* Capacitance (C):
* F
  mF
  µF
  nF
  pF

* Voltage (V):
* V
  mV
  kV

* Energy (E):
* J
  mJ
  µJ
  kJ

Please fill in exactly two variables.

Calculate



Energy Stored in a Capacitor — Explanation
------------------------------------------

When a voltage \( V \) is applied across a capacitor with capacitance \( C \), charge accumulates on the plates and energy is stored in the electric field between them. The energy stored is:
\[
E = \frac{1}{2} C V^2
\]
Where:

* \( E \) is the stored energy (in Joules, \( \text{J} \)),
* \( C \) is the capacitance (in Farads, \( \text{F} \)),
* \( V \) is the voltage across the capacitor (in Volts, \( \text{V} \)).

The \( V^2 \) dependence is the key insight: doubling the voltage quadruples the stored energy. This is why high-voltage capacitors are so effective in pulsed energy applications like camera flashes or defibrillators.

The stored charge \( Q \) on the plates follows directly from the definition of capacitance:
\[
Q = C \cdot V
\]
Substituting this into the energy formula gives two equivalent forms:
\[
E = \frac{Q^2}{2C} = \frac{1}{2} Q V
\]
All three forms are equivalent — which one to use depends on what variables are known.

Purpose of the Calculator
-------------------------

Given any two of the three variables \( E \), \( C \), and \( V \), the calculator solves for the missing one. The rearranged formulas are:

* To solve for \( E \) (energy):
  \[
  E = \frac{1}{2} C V^2
  \]
* To solve for \( C \) (capacitance):
  \[
  C = \frac{2E}{V^2}
  \]
* To solve for \( V \) (voltage):
  \[
  V = \sqrt{\frac{2E}{C}}
  \]

In all cases, the stored charge \( Q = C \cdot V \) is shown as an additional output.

More info
---------

Looking for more helpful tools and calculators? Explore a wide range of resources to simplify your engineering projects and calculations. Head over to our [tools section](https://blog.hirnschall.net/tools/) to find our free online calculators.  
For actual projects and informational articles head over to [blog.hirnschall.net](https://blog.hirnschall.net/).