What is the formula for energy stored in a capacitor?

The energy stored in a capacitor is E = ½CV², where E is energy in joules, C is capacitance in farads, and V is the voltage across the capacitor in volts. The factor of ½ arises because the charge builds up gradually as voltage increases from 0 to V.

Why does energy depend on voltage squared?

Energy scales with V² because each additional unit of charge deposited on the capacitor requires more work as the existing charge already creates a repelling electric field. Doubling the voltage quadruples the stored energy, making voltage rating the dominant factor in energy storage.

What units does this calculator support?

Capacitance: farads (F), millifarads (mF), microfarads (µF), nanofarads (nF), and picofarads (pF). Voltage: volts (V), kilovolts (kV), and millivolts (mV). Energy output is shown in joules (J), millijoules (mJ), microjoules (µJ), and kilojoules (kJ).

How do I solve for capacitance or voltage?

Switch the "Solve for" selector to Capacitance or Voltage. For capacitance: C = 2E ÷ V². For voltage: V = √(2E ÷ C). Enter the two known values and the calculator rearranges the formula automatically.

What is a typical capacitor energy value?

A 100 µF capacitor charged to 12 V stores about 7.2 mJ. A 1000 µF capacitor at 400 V (common in camera flashes) stores 80 J. Supercapacitors can reach hundreds of farads and store kilojoules at low voltages. Energy scales dramatically with both capacitance and voltage.

Capacitor Energy Calculator

Name: Capacitor Energy Calculator
Availability: InStock
Author: Nham Vu

Calculate energy stored in a capacitor (E = ½CV²) or solve for capacitance or voltage, with full unit support.

Capacitor Energy Calculator

Solve for

Capacitance

Voltage

E = ½ × C × V²

Enter two known values on the left to compute the result.

E = ½CV²

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Summary

Calculate energy stored in a capacitor (E = ½CV²) or solve for capacitance or voltage, with full unit support.

How it works

Select what you want to solve for: Energy, Capacitance, or Voltage.
Enter the two known values and select their units from the dropdowns.
The result appears instantly along with all unit conversions.
Click any conversion card to copy that value to your clipboard.
Use the Clear button to reset inputs and start a new calculation.

Use cases

Calculate the energy stored in a capacitor bank for a power supply design.
Determine what capacitance is needed to store a target energy at a given voltage.
Find the voltage required across a capacitor to achieve a specific stored energy.
Compare energy storage across different capacitor values and ratings.
Solve physics homework problems involving capacitors and electric fields.
Estimate charge/discharge energy in camera flash circuits.
Analyze energy in filter or decoupling capacitors in electronics design.
Convert capacitor energy results between joules, millijoules, and microjoules.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu