How to use this calculator
- Enter or choose capacitance.
- Enter or choose capacitance unit.
- Enter or choose voltage across the capacitor.
- The stored energy updates as you type. Use Copy result or Share to keep it.
Method
E = ½ × C × V²; Q = C × V; Wh = J ÷ 3600
- C
- capacitance in farads
- V
- voltage in volts
- E
- energy in joules
- Q
- charge in coulombs
Worked example
- C = 1000 µF = 0.001 F.
- E = ½ × 0.001 × 50² = 1.25 J.
- Q = 0.001 × 50 = 0.05 C = 50 mC.
A 1000 µF capacitor charged to 50 V stores 1.25 J and holds 50 mC of charge.
What the result means
Only part of this energy is usable if the load stops working below some minimum voltage: usable energy = ½C(V₁² − V₂²).
Assumptions and limits
- Ideal capacitor with constant capacitance.
- Leakage, ESR losses and capacitance tolerance (often ±20%) are not included.
Questions
Is a charged capacitor dangerous?
Large capacitors at high voltage can deliver a dangerous shock long after power is removed. Discharge them through a suitable resistor before handling.
Why only half of CV²?
The voltage rises from 0 to V as charge is added, so the average voltage during charging is V ÷ 2.