Stored electrical energy
What is capacitor energy?
A charged capacitor stores electrical potential energy in the electric field between its conductors.
The stored energy depends on the capacitor's capacitance, voltage, and charge. This calculator supports the three standard equivalent energy formulas.
Equivalent equations
Capacitor energy formulas
From capacitance and voltageU = ½CV²
From charge and voltageU = ½QV
From charge and capacitanceU = Q² ÷ 2C
- U is stored energy in joules.
- C is capacitance in farads.
- Q is electric charge in coulombs.
- V is voltage in volts.
Worked example
Calculate energy from capacitance and voltage
Suppose a capacitor has a capacitance of 2 μF and a voltage of 12 V.
- Convert 2 μF to 0.000002 F.
- Use U = ½CV².
- Substitute C = 0.000002 and V = 12.
- U = ½ × 0.000002 × 12².
- The stored energy is 0.000144 J.
Voltage effect
Why voltage has a strong effect
In U = ½CV², voltage is squared. This means doubling voltage increases stored energy by a factor of four when capacitance remains constant.
Real capacitors have rated voltage limits. Exceeding the manufacturer's rating can damage the dielectric and create a safety hazard.
SI unit guidance
Capacitor energy units
- Energy: joules (J).
- Capacitance: farads (F).
- Charge: coulombs (C).
- Voltage: volts (V).
- 1 microfarad = 1 × 10⁻⁶ F.
- 1 millijoule = 1 × 10⁻³ J.
Practical uses
Where capacitor energy matters
- Camera flashes and pulse circuits.
- Power-supply smoothing and backup.
- Defibrillators and pulsed medical equipment.
- Electric vehicle and industrial power electronics.
- Laboratory demonstrations of electrical energy storage.
Model limitations
Assumptions and limitations
- The capacitor is treated as ideal.
- Leakage current is not included.
- Equivalent series resistance is not included.
- Dielectric heating and losses are ignored.
- All inputs are treated as positive magnitudes.
Common questions
Capacitor energy calculator FAQ
What formulas does the capacitor energy calculator use?
It uses U = 1/2 CV², U = 1/2 QV, and U = Q²/(2C), depending on which two capacitor values are known.
What is the unit of energy stored in a capacitor?
Capacitor energy is measured in joules, written J.
How do I calculate capacitor energy from capacitance and voltage?
Multiply one-half by capacitance and by the square of voltage using U = 1/2 CV².
Why does capacitor energy depend on voltage squared?
As voltage increases, both the stored charge and the energy per unit charge increase, so total stored energy grows with V².
Is this the same as a capacitance calculator?
No. A capacitance calculator focuses on C = Q/V. This calculator focuses on stored electrical energy and related rearrangements.