Stored charge
Q = CV
Charge is capacitance times voltage.
Capacitor Energy Calculator
Calculate capacitor charge and ideal stored electrostatic energy from capacitance and terminal voltage.
Access: Free to use, no installation, and No account required.
Inputs
The ideal energy equation does not include ESR heating, leakage, dielectric absorption, voltage derating, ripple-current limits, or capacitor tolerance.
Results
Stored energy
Ideal capacitor energy is E = ½CV², while stored charge is Q = CV. Energy therefore rises with the square of voltage.
Engineering reference
Capacitor Energy Calculator: background and worked detail
Use the Capacitor Energy Calculator to calculate ideal stored charge and electrostatic energy from capacitance and voltage.
Stored energy and charge
Stored energy
E = ½CV²
Electrostatic energy rises with the square of voltage.
Engineering theory and interpretation
An ideal capacitor stores charge proportional to voltage and energy proportional to the square of voltage. Because energy scales as V², increasing capacitor voltage has a much larger energy effect than an equal percentage increase in capacitance.
Real capacitors have voltage ratings, ESR, leakage, dielectric absorption, capacitance tolerance, ripple-current limits, temperature dependence, and discharge hazards that are not captured by the ideal energy equation.
1,000 µF charged to 12 V
Use capacitance 1,000 µF and voltage 12 V.
- Convert 1,000 µF to 0.001 F.
- Q = 0.001 × 12 = 0.012 C.
- E = 0.5 × 0.001 × 12² = 0.072 J.
Result: The stored energy is 0.072 J, equivalent to 0.000020 Wh.
Validation checks
The quadratic voltage dependence makes these checks quick to confirm.
Voltage scaling
Case: Double voltage with capacitance unchanged.
Expected: Stored charge should double and stored energy should quadruple.
Capacitance scaling
Case: Double capacitance with voltage unchanged.
Expected: Stored charge and stored energy should both double.
Assumptions and model boundaries
Assumptions
- An ideal lumped capacitor with constant capacitance.
- Voltage is within the mathematical model and represented as a scalar terminal voltage.
- Energy is electrostatic stored energy only.
Limitations
- Does not account for ESR loss, leakage, dielectric absorption, voltage coefficient, or capacitance tolerance.
- Does not determine safe discharge time, arc energy, fuse requirements, or capacitor bank fault behavior.
Capacitor Energy Calculator FAQ
Why does capacitor energy depend on voltage squared?
The incremental energy needed to add charge rises as capacitor voltage rises; integrating that charging work gives E = ½CV².
Is all stored energy recoverable?
Not in a real circuit. ESR, leakage, switching loss, residual voltage, and converter limits reduce recoverable energy.
Can a charged capacitor be hazardous?
Yes. Even modest capacitance can store hazardous energy at high voltage. Use appropriate discharge, insulation, enclosure, and safety procedures.
Where this calculation comes from
Shared with the Capacitors and Inductors Workbench.
Open the source workbench →Read calculation and source methodology →