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Capacitor Charge, Voltage & Stored Energy

Relate positive capacitance, voltage, charge and energy in an ideal linear capacitor.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

A 2 F capacitor at 3 V holds charge 6 C and stores 9 J of energy.

Q = CV; stored energy = ½CV²

Worked example

Enter these known values and leave the other values blank.

Capacitance
2 F
Voltage magnitude
3 V
Charge magnitude
6 C
Stored electric energy
9 J

Assumptions and limitations

  • This is an ideal component model. Losses, tolerances, temperature dependence, parasitics and component ratings require separate information.
  • All quantities must be strictly positive in the retained magnitude-only model. Zero charge and signed polarity are outside its input domain.
  • The capacitance is constant over the voltage range. Energy scales with voltage squared, and the result is stored energy, not an instantaneous power.
  • The elementary-charge unit uses exactly 1.602176634 × 10⁻¹⁹ coulomb. It is a unit conversion, not an assertion that the macroscopic input has been quantized.

Common questions

Why is energy not simply charge times final voltage?

For a linear capacitor charged from zero, voltage increases as charge is added. The average charging voltage is half the final voltage, giving ½QV.

How does doubling voltage affect energy?

At fixed capacitance, it multiplies stored energy by four.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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