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Energy Stored in a Capacitor

E=12CV2E = \tfrac{1}{2} C V^{2}
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Worked example: 100 uF at 12 V → 7.2 mJ. Press Try an example to run it live, then adjust anything.

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See also

Capacitance (C = Q/V): Both use electrical capacitance and capacitor voltage.RC Capacitor Charging: Both use capacitor voltage.RC Capacitor Discharge: Both use capacitor voltage.Power-Factor Correction Capacitance: Both use capacitor voltage.Capacitive Reactance (X_C = 1/2πfC): Both use electrical capacitance.LC Resonant Frequency: Both use electrical capacitance.
3 more relatedRC Time Constant: Both use electrical capacitance.Two Capacitors in Parallel: Both use electrical capacitance.Two Capacitors in Series: Both use electrical capacitance.
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Energy Stored in a Capacitor explained

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Why the half? Charging a capacitor is like stretching a spring: the first coulomb slides on easily, but every later coulomb must be pushed against the voltage the earlier ones built up. The voltage ramps linearly from 0 to V as charge accumulates, so the average push is V/2, and the total work is Q×V/2 = ½CV²: the triangular area under the Q–V line. Equivalent forms E = Q²/(2C) and E = QV/2 follow directly from C = Q/V.

Worked example: a camera-flash capacitor of 1000 µF charged to 300 V stores E = ½ × 0.001 × 300² = 45 J, dumped through the xenon tube in about a millisecond, a burst of tens of kilowatts from a pocket battery. The same math sizes defibrillators and grid-scale supercapacitor banks. Solving for V takes the positive square root, since the formula gives the voltage magnitude.

Energy Stored in a Capacitor formula

E=12CV2E = \tfrac{1}{2} C V^{2}
Where
  • EE= Stored energy (J)
  • CC= Capacitance (μF)
  • VV= Voltage (V)
Revised 16 October 2026
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formula.expert. (2026, October 16). Energy Stored in a Capacitor Formula & Calculator. https://formula.expert/solvers/capacitor-energy

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