Calculators
Capacitor Energy Calculator
Calculate energy stored in a capacitor from capacitance and voltage.
Capacitor Energy Calculator tool
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About This Tool
A charged capacitor stores electrostatic energy in the electric field between its conductors. This calculator finds the ideal stored energy when capacitance and voltage are known. It is useful for electronics study, checking circuit calculations, comparing capacitor values, and understanding why stored energy rises quickly as voltage increases. The calculation runs locally in your browser and uses E = ½CV².
How To Use It
- Enter the capacitor's capacitance and choose the matching farad-based unit.
- Enter the voltage across the capacitor and select volts, millivolts, or kilovolts.
- Choose the energy output unit and read the calculated stored energy.
- Use the result as an ideal calculation; real components have ratings, tolerances, losses, and safety constraints.
Examples
100 µF at 12 V
For C = 100 µF and V = 12 V, E = ½ × 0.0001 × 12² = 0.0072 J, which is 7.2 mJ.
Voltage has a squared effect
If capacitance stays fixed and voltage doubles, stored energy becomes four times as large because voltage is squared in E = ½CV².
Zero voltage
An ideal capacitor with zero voltage across it has zero stored electrostatic energy, regardless of its capacitance value.
Useful Notes
Stored-energy formula
The ideal capacitor energy formula is E = ½CV², where E is energy in joules, C is capacitance in farads, and V is the voltage across the capacitor in volts.
Why voltage is squared
Energy increases with the square of voltage. Increasing voltage from 5 V to 10 V at the same capacitance multiplies stored energy by four, not two.
Voltage polarity and energy
Changing voltage polarity does not make stored energy negative because V is squared. Polarity matters elsewhere in circuits and for polarized capacitor types, but the ideal stored-energy magnitude remains non-negative.
Unit conversion
Capacitance is converted to farads and voltage to volts before calculation. The result is computed in joules and can then be displayed in joules, millijoules, microjoules, or kilojoules.
Ideal model and practical limits
The formula describes ideal electrostatic energy. Real capacitors have capacitance tolerance, equivalent series resistance, leakage, dielectric losses, voltage ratings, temperature limits, and discharge behavior that this calculator does not model. A stored-energy result is not a safety rating.
FAQ
What is the formula for energy stored in a capacitor?
For an ideal capacitor, stored energy is E = ½CV², with capacitance in farads and voltage in volts to obtain joules.
Does a negative voltage produce negative capacitor energy?
No. Voltage is squared in the energy formula, so reversing voltage polarity gives the same ideal stored-energy magnitude.
What happens to energy if voltage doubles?
At constant capacitance, doubling voltage makes stored energy four times larger because energy is proportional to V².
Can this calculator determine whether a capacitor is safe to use?
No. It calculates ideal stored energy only. Component selection also requires voltage rating, capacitance tolerance, ESR, ripple current, temperature, discharge conditions, manufacturer specifications, and appropriate electrical safety practices.