What is the formula for energy stored in a capacitor?

The energy is E = ½ × C × V², where C is the capacitance in farads and V is the voltage in volts. The result is in joules.

Why does doubling the voltage quadruple the stored energy?

Because voltage is squared in the formula. If V doubles, V² increases by a factor of 4, so the stored energy increases fourfold. This is why high-voltage capacitors store much more energy than low-voltage ones of the same capacitance.

What units can I enter for capacitance?

This calculator accepts farads (F), millifarads (mF), microfarads (µF), nanofarads (nF), and picofarads (pF). Select the correct unit from the dropdown before entering the value.

Is there an equivalent formula using charge instead of voltage?

Yes. Since Q = C × V, you can also write E = Q² / (2C) or E = ½ × Q × V, where Q is the charge in coulombs. All three forms are mathematically equivalent.

What voltage should I use for a charged capacitor in a real circuit?

Use the voltage across the capacitor terminals at the moment you want to measure. For a fully charged capacitor connected to a supply, this equals the supply voltage.

Energy Stored in a Capacitor Calculator

Enter capacitance and voltage to calculate the energy stored in a capacitor using E = ½CV².

Inputs

Capacitance (C)

Voltage (V) — volts

Formula

E = ½ × C × V²

E in joules, C in farads, V in volts

Result

Enter values and click Calculate

Copied!

Summary

This calculator applies the standard formula E = ½ × C × V² to find how much energy a capacitor holds at a given voltage. Enter capacitance in any common unit (F down to pF) and voltage in volts, and the tool returns the result in joules along with millijoule and microjoule equivalents for easier reading at small scales.

How it works

Enter the capacitance value and select its unit.
Enter the voltage across the capacitor.
The calculator converts capacitance to farads, then computes E = ½ × C × V².
Results are displayed in joules, millijoules, and microjoules.

Use cases

Design energy storage circuits with the correct capacitor rating.
Estimate the energy released by a capacitor bank during a discharge.
Verify textbook physics problems involving electric potential energy.
Compare energy densities when selecting capacitors for power supply designs.
Calculate stored energy in flash capacitors used in cameras or defibrillators.
Understand energy trade-offs between capacitance and voltage in circuit design.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu