Electronics · Capacitors
Capacitor energy calculator.
Enter a capacitance and the voltage across it to see the energy and charge it holds.
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Capacitor energy formula
The energy stored in a capacitor is E = ½ × C × V², in joules when C is in farads and V is in volts. The charge on it is Q = C × V, in coulombs. Energy also equals ½QV, or Q² ÷ 2C.
Worked example. A 1,000 µF capacitor charged to 12 V: E = 0.5 × 0.001 × 144 = 0.072 J, and Q = 0.001 × 12 = 0.012 C.
Doubling the voltage quadruples the energy. The result is the ideal stored energy, not what a circuit can deliver: real capacitors have leakage, ESR and a voltage rating you must stay under.
Frequently asked questions
How do you calculate the energy stored in a capacitor?
E = ½ C V². For 1,000 µF at 12 V that is 0.072 joules.
What is the charge on a capacitor?
Q = C × V. The same 1,000 µF at 12 V holds 0.012 coulombs.
Why does voltage matter more than capacitance for energy?
Energy grows with the square of voltage but only linearly with capacitance, so doubling voltage gives four times the energy.
Can I use more than the rated voltage?
No. Stay at or below the voltage printed on the part. Charged large capacitors can also deliver a harmful discharge, so discharge them safely before handling.
Is all the stored energy usable?
No. A circuit only gets the energy while the voltage is above what it needs, and losses in ESR and wiring reduce it further.
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Scope and safety
Low-voltage hobby and study use only. Results are ideal-component arithmetic from the formulas shown, not an engineering design or professional advice. Real parts vary with tolerance, temperature and age, so check the datasheet for every part. Never work on mains-powered circuits from a calculator result, and discharge large capacitors safely before handling.