Capacitor Energy Calculator

Frequently Asked Questions

How much energy does a capacitor store?

E = ½·C·V², so energy rises with the square of the voltage - doubling voltage quadruples stored energy.

What is the stored charge?

Q = C·V; this calculator reports both the charge in coulombs and the energy in joules.

Why does voltage matter more than capacitance?

Because energy is linear in C but quadratic in V, raising voltage is the most effective way to store more energy (within the rated limit).

Where is this used?

Camera flashes, defibrillators, power-supply smoothing, and energy-recovery systems all rely on stored capacitor energy.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

A charged capacitor stores energy in the electric field between its plates. The energy is E = ½CV², which is equivalent to E = ½QV and E = Q² ÷ (2C), since charge and voltage are tied by Q = CV. Here C is capacitance in farads, V is the voltage across the plates, and Q is the stored charge in coulombs. This calculator takes capacitance in microfarads (µF) - the common practical unit - converts internally to farads, and solves for energy, capacitance, voltage, or charge given the others. Results appear in joules and millijoules for energy, and coulombs and microcoulombs for charge.

Worked Example: A Camera Flash Capacitor

A 1000 µF capacitor charged to 12 V stores E = ½ × (1000 × 10⁻⁶ F) × 12² = ½ × 0.001 × 144 = 0.072 J = 72 mJ. Its charge is Q = CV = 0.001 × 12 = 0.012 C = 12,000 µC. Because energy scales with the square of voltage, doubling to 24 V quadruples the stored energy to 288 mJ - this is why high-voltage capacitor banks in defibrillators and camera flashes pack so much energy into a small device, and why a charged high-voltage capacitor can deliver a dangerous shock long after power is removed.

Real-World Uses

Camera flashes & strobes: dump tens of joules into a xenon tube in milliseconds.

Defibrillators: deliver a precisely controlled energy pulse (typically 150–360 J).

Power-supply smoothing: bulk capacitors ride through brief input dropouts.

Energy harvesting & backup: supercapacitors store charge for memory retention.

Common Mistakes

The most common error is forgetting the factor of ½ - it appears because voltage builds from zero to V as charge accumulates, so the average voltage during charging is V÷2. Another is unit confusion: capacitance is often labelled in µF, nF, or pF, and mixing these with farads throws the answer off by orders of magnitude. This calculator handles the µF→F conversion for you. Treating Q = CV as if Q stayed constant when voltage changes is also wrong unless the capacitor is isolated.

Limitations & Related

This computes stored energy and charge for an ideal capacitor - it is distinct from a reactance or impedance calculator, which deals with how a capacitor opposes alternating current (Xᶜ = 1 ÷ (2πfC)). Real capacitors have equivalent series resistance, leakage, a finite breakdown voltage, and capacitance that drifts with temperature and applied voltage (especially ceramic types). Electrolytic capacitors are polarised and fail if reverse-biased. For energy delivered into a load, also account for circuit resistance and discharge time - see the RC time-constant calculator.

Capacitor Energy Calculator

Frequently Asked Questions

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