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A capacitor stores energy in its electric field, proportional to its capacitance and the square of the voltage across it. This calculator solves for whichever value — capacitance, voltage, or stored energy — is missing.
How it works
Enter any 2 of the 3 values (capacitance in microfarads, voltage, or energy in millijoules) and leave the one you want to solve for blank. The calculator applies E = ½CV².
- Enter capacitance (µF) — leave blank to solve for this.
- Enter voltage (V) — leave blank to solve for this.
- Enter energy (mJ) — leave blank to solve for this.
- Click Calculate to see your results.
Examples
A charged capacitor
A 100 µF capacitor charged to 12V stores about 7.2 millijoules of energy.
Who should use it
- Electronics coursework on capacitor behavior.
- Estimating stored energy for capacitor-based circuit design (e.g. flash circuits, energy storage).
Industry applications
- Electronics and circuit design
- Power electronics and energy storage
Advantages
- Solves for any of the three variables, not just forward energy calculation.
- Simple, exact formula for ideal capacitor behavior.
Limitations
- Assumes an ideal capacitor — real capacitors have some energy loss (equivalent series resistance) not captured by this idealized formula.
Common mistakes to avoid
- Assuming energy scales linearly with voltage — it scales with the square of voltage, so doubling voltage quadruples stored energy.
- Mixing up energy (joules) with charge (coulombs) — they're related but answer different questions.
Best practices
- Remember that doubling voltage across a capacitor quadruples its stored energy, not just doubles it — a common intuition trap.
- Use this alongside a capacitor's voltage rating to check it's operating safely within its rated limits.
Tips
- If you're designing for a target stored energy, solving for voltage given a known capacitor's capacitance is often more practical than assuming a voltage first.