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Capacitor Calculator

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Find the energy and charge stored in a capacitor, or the combined capacitance of two capacitors wired in series or parallel.

Capacitor Calculator

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Stored energy
0.072 J
Stored charge
12 mC

The formulas

Stored energy: E = 0.5 x C x V^2 (Joules, with C in Farads) Stored charge: Q = C x V (Coulombs) Parallel combination: C_total = C1 + C2 Series combination: C_total = (C1 x C2) / (C1 + C2)
Example

A 1,000µF capacitor charged to 12V: energy = 0.5 x 0.001 x 144 = 0.072 J, storing 12 mC of charge.

Step-by-step guide

  1. Choose stored energy or combining two capacitors.
  2. For stored energy: enter the capacitor's value in microfarads and its charged voltage.
  3. For combining: enter both capacitor values and choose series or parallel wiring.

Why series and parallel work opposite to resistors

This often trips people up coming from resistor math: capacitors in parallel simply add together (like resistors in series), while capacitors in series combine like resistors in parallel - using the reciprocal formula. The physical reason is that parallel capacitor plates effectively increase total plate area (more capacitance), while series capacitors effectively increase total plate separation (less capacitance).

Common mistakes

Applying the resistor series/parallel formulas directly to capacitors - they're reversed compared to resistors, a very common source of errors.
Forgetting to convert microfarads to farads before calculating energy - the formula needs base units (Farads), not microfarads, or the result will be off by a factor of a million.

Frequently asked questions

What's the practical difference between charge and stored energy?

Charge (in coulombs) measures the total quantity of electrical charge stored, while energy (in joules) measures the actual work that charge can do - energy scales with voltage squared, while charge scales linearly with voltage.

Why do series capacitors have a lower combined capacitance than either one alone?

Wiring capacitors in series effectively increases the distance between the outermost plates, which reduces the overall capacitance below either individual capacitor's value - always true for series combinations.

Is it safe to discharge a large capacitor by shorting it?

Large or high-voltage capacitors can store significant, potentially dangerous energy - use a proper discharge resistor and appropriate safety precautions rather than shorting them directly, especially for capacitors from power supplies or automotive systems.

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