Capacitor Energy Calculator
Find energy, charge, and required capacitance.
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Formulas
E = ½ × C × V²Energy in Joules
Q = C × VCharge in Coulombs
Capacitor Energy
Doubling voltage quadruples energy. A 1000μF cap at 50V stores 1.25J. A supercapacitor (1F, 2.7V) stores 3.65J. A AA battery stores ~10,000J.
Energy Stored in a Capacitor
A charged capacitor stores energy in the electric field between its plates. That stored energy depends on the capacitance and the square of the voltage:
E = ½ × C × V²E is energy in joules, C is capacitance in farads, V is the voltage across the capacitor.
Because energy scales with voltage squared, doubling the voltage stores four times the energy. This is why capacitor voltage ratings matter so much.
Worked Examples
C = 1000 µF charged to 25 V:
E = 0.5 × 0.001 × 25² = 0.31 J
Same capacitor at 50 V:
E = 0.5 × 0.001 × 50² = 1.25 J — four times the energy.
Where This Matters
Stored energy determines how much charge a capacitor can deliver during a power interruption, the flash energy in a camera, or the hazard from a charged high-voltage capacitor. Large capacitors at high voltage can hold dangerous energy even after the supply is removed, which is why they are bled through discharge resistors before servicing.
Frequently Asked Questions
Why is there a factor of one-half?
Voltage builds up gradually as the capacitor charges, so the average voltage during charging is half the final value. Integrating charge against voltage yields the ½CV² result.
Is a charged capacitor dangerous?
It can be. High-voltage capacitors store enough energy to cause a shock or spark long after power is off. Always discharge large capacitors safely before handling.
How does this relate to charge?
Charge is Q = CV. Energy can also be written E = ½QV or E = Q²/(2C), all equivalent forms.