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Capacitance for Ideal Stored Energy

Calculate ideal capacitance from a positive stored-energy target and voltage magnitude.

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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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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Storing 50 μJ at 10 V requires an ideal capacitance of 1 μF.

Capacitance = 2 × stored energy / voltage²

Worked example

Enter these known values and leave the other values blank.

Ideal stored energy
50 μJ
Voltage magnitude
10 V
Ideal capacitance
1 μF

Assumptions and limitations

  • This is an ideal component model. Losses, tolerances, temperature dependence, parasitics and component ratings require separate information.
  • Energy, voltage and capacitance must be positive. The initial energy unit is microjoules and the initial capacitance unit is microfarads.
  • The energy is total energy stored relative to zero voltage. If a load must remain above a minimum voltage, only ½C(Vstart² − Vend²) is available between those voltages.
  • This calculation does not select a component voltage rating, assess ripple current or determine a motor starting capacitor.

Common questions

Does all stored energy remain usable above a minimum voltage?

No. Some energy remains when the capacitor reaches that minimum. Use the difference between initial and final stored energies for a specified discharge range.

Can I solve voltage from energy and capacitance?

Yes. The inverse returns the positive voltage magnitude √(2E/C).

References

Bookify requires positive capacitance in the positive-energy capacitor model.

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