Capacitor Energy Storage Calculator
Calculate energy stored in a capacitor using E = 0.5*C*V^2.
Returns energy in joules, millijoules, and charge in coulombs for any capacitance and voltage.
A capacitor stores energy in its electric field between the plates. The stored energy and charge are:
E = ½CV² Q = CV
Where:
- E = Energy in joules (J)
- Q = Charge in coulombs (C)
- C = Capacitance in farads (F)
- V = Voltage across the capacitor (V)
Key observations:
- Energy scales with the square of voltage: doubling voltage quadruples stored energy
- This is why high-voltage capacitors are so dangerous. 400 V × 100 μF = ½ × 0.0001 × 160,000 = 8 joules, enough to cause a severe shock
Comparison with inductors:
- Capacitor stores energy in electric field: E = ½CV²
- Inductor stores energy in magnetic field: E = ½LI²
- They are the “dual” of each other in circuit theory
Practical examples:
| Application | Capacitance | Voltage | Energy |
|---|---|---|---|
| Camera flash | 100 μF | 300 V | 4.5 J |
| Car audio capacitor | 1 F | 12 V | 72 J |
| Supercapacitor (EV braking) | 3000 F | 2.7 V | 10,935 J ≈ 3 Wh |
| Defibrillator | 30 μF | 5000 V | 375 J |
| Laptop battery (comparison) | n/a | n/a | ~50,000 J = 14 Wh |
Safety warning
Capacitors can hold their charge long after the power is removed. Large electrolytic caps in switching power supplies, microwave ovens, CRTs, and air conditioners can deliver lethal shocks even when the unit is unplugged. Always discharge through a bleeder resistor before handling. Never short the terminals with metal, which can weld the conductor and explode the capacitor case.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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