Capacitor Energy Calculator

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. To model how that energy is delivered over time as the capacitor discharges, use the capacitor discharge calculator.

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. If C needs to be derived from plate geometry first, use the parallel plate capacitor calculator.

Related Tools

• Capacitor Discharge Calculator — compute voltage and current as stored energy is released.
• Parallel Plate Capacitor Calculator — derive C from plate geometry and dielectric constant.
• Capacitors in Series / Capacitors in Parallel — find the equivalent C for a capacitor network.
• Inductor Energy Calculator — the inductive equivalent: \( E = \frac{1}{2}LI^2 \).

More calculators: blog.hirnschall.net/tools/.