Capacitor Energy Calculator

Capacitor energy refers to the electrical energy stored in the electric field between a capacitor’s plates. This energy can be released quickly, which makes capacitors essential in cameras (flash), defibrillators, power supplies, and countless electronic circuits.

The formula:

E = ½ × C × V²

Where:

• E = energy stored (in Joules)
• C = capacitance (in Farads)
• V = voltage across the capacitor (in Volts)

Alternative forms:

• E = Q² / (2C) — when you know the charge Q (in Coulombs)
• E = ½ × Q × V — when you know both charge and voltage

The charge on a capacitor is: Q = C × V

Capacitance units: Farads (F) are very large. In practice, most capacitors are measured in smaller units:

• 1 microfarad (μF) = 10⁻⁶ F = 0.000001 F
• 1 nanofarad (nF) = 10⁻⁹ F = 0.000000001 F
• 1 picofarad (pF) = 10⁻¹² F = 0.000000000001 F
• Supercapacitors can reach 1–3000 F

Energy units:

• 1 Joule (J) = 1000 millijoules (mJ)
• 1 millijoule (mJ) = 1000 microjoules (μJ)

Practical examples:

• A 100μF capacitor at 50V stores 0.125 J — enough to give you a noticeable shock.
• A camera flash capacitor (about 300μF at 300V) stores 13.5 J — enough for a bright flash.
• A defibrillator capacitor stores about 200–360 J — enough to restart a heart.
• A 1F supercapacitor at 5V stores 12.5 J.

Why does voltage matter so much? Notice that energy depends on voltage squared (V²). Doubling the voltage quadruples the stored energy. This is why high-voltage capacitors are treated with extreme caution — even a small capacitor at high voltage can store dangerous amounts of energy.

Safety warning: Capacitors can hold a charge long after power is removed. Large capacitors in power supplies, air conditioners, and microwave ovens can deliver lethal shocks even when unplugged. Always discharge capacitors safely before handling.

This calculator lets you select capacitance in μF, nF, or pF for convenience, and shows the result in joules, millijoules, and microjoules.