Electronics Calculator

Capacitor Energy Calculator

Calculate the energy stored in a capacitor from capacitance and voltage using E = ½CV². You can also calculate the required capacitance or voltage when the desired energy is known.

Capacitor Energy

Select what you want to calculate and enter the known electrical values.

Calculation mode
V
In Energy mode this field is calculated automatically from C and V.
Quick presets
Key relationship
Capacitor energy increases linearly with capacitance but with the square of voltage: E = ½CV² .

Results

Calculated capacitor energy and related electrical quantities.

Stored Energy
—
E = ½CV²
Capacitance
—
C
Voltage
—
V
Charge
—
Q = CV
Energy
—
Joules
Voltage Squared
—
V²
Derived value

Capacitor Energy Formula

A capacitor stores electrical energy in the electric field between its conductive plates. The stored energy depends on both capacitance and voltage.

E = ½CV²
E = energy in joules, C = capacitance in farads, V = voltage in volts

From Charge

E = ½QV
Q = stored charge in coulombs

Calculating Required Capacitance

C = 2E / V²
Used when desired energy and voltage are known

Calculating Required Voltage

V = √(2E / C)
Used when desired energy and capacitance are known

How Capacitor Energy Works

When a voltage is applied to a capacitor, electric charge accumulates on its plates. The resulting electric field stores energy.

The relationship is especially sensitive to voltage because voltage is squared in the formula.

Example: 100 nF at 12 V

E = ½ × 100 nF × (12 V)²

E = 0.5 × 100 × 10⁻⁹ × 144

E = 7.2 µJ

Doubling Voltage

If the capacitance stays constant and voltage doubles, the stored energy becomes four times greater.

For example, increasing a capacitor from 10 V to 20 V changes V² from 100 to 400. The stored energy therefore increases by a factor of four, assuming the capacitor can safely withstand the higher voltage.

Energy Stored in a Capacitor

The energy is stored in the electric field between the capacitor's plates. Increasing capacitance increases the amount of charge that can be stored at a given voltage.

+Q −Q Electric field stores energy

Applications of Capacitor Energy

  • Flash and pulse-power circuits.
  • Camera flash energy storage.
  • DC-link and power-electronics capacitor banks.
  • Backup and hold-up power circuits.
  • Energy buffering in power supplies.
  • Motor-starting and pulse applications.
  • Resonant circuits and RF systems.
  • Energy storage experiments and educational electronics projects.

Practical Design Considerations

Voltage Rating

Never operate a capacitor above its specified voltage rating. The theoretical energy formula does not override the component's electrical limits.

Tolerance

Real capacitor values vary from their nominal marked capacitance. The actual stored energy therefore also varies.

Leakage Current

Real capacitors are not perfect energy storage devices. Leakage current causes stored charge and energy to decrease over time.

ESR and Heating

Equivalent series resistance can cause losses and heating, particularly when the capacitor experiences significant ripple current.

Discharge Safety

A charged capacitor can retain potentially hazardous energy after the power source has been disconnected. Appropriate discharge and electrical safety procedures are important when working with larger capacitors and capacitor banks.

Capacitor Energy Examples

Example 1: Small Capacitor

C = 100 nF
V = 12 V

E = ½ × 100 nF × 12²

E = 7.2 µJ

Example 2: Electrolytic Capacitor

C = 1000 µF
V = 25 V

E = ½ × 0.001 × 625

E = 0.3125 J

Example 3: Energy to Capacitance

E = 1 J
V = 100 V

C = 2E / V²
C = 2 / 10000

C = 200 µF

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Capacitor Energy Calculator FAQ

Common questions about capacitor energy, charge, capacitance and voltage.

The energy stored in a capacitor is calculated with E = ½CV², where E is energy in joules, C is capacitance in farads and V is voltage in volts.
The standard capacitor energy formula is E = ½CV². The voltage is squared, so increasing voltage has a strong effect on stored energy.
Using E = ½CV², a 1 µF capacitor charged to 10 V stores 0.00005 J, or 50 µJ.
Energy is proportional to the square of voltage. If capacitance stays constant and voltage doubles, stored energy increases by a factor of four.
At a fixed voltage, stored energy is directly proportional to capacitance. Doubling capacitance doubles the stored energy.
Yes. Because Q = CV, capacitor energy can also be calculated as E = ½QV.
Energy is measured in joules (J). Small capacitors commonly store energy in microjoules or millijoules, while large capacitor banks can store substantially more energy.
Yes. A capacitor must not be operated above its rated voltage. The theoretical stored energy increases with voltage, but the actual usable energy is constrained by the component voltage rating and other practical limits.