Capacitors store energy in an electric field and can release it very quickly, as in camera flashes and defibrillators.
How to use the Capacitor Energy Calculator
- Capacitance
- Voltage
- Want to work backwards? Type a value into Stored energy and Voltage is calculated for you.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Multiply half the capacitance by the square of the voltage.
Inputs explained
| Field | What to enter |
|---|---|
| Capacitance | Units: µF, nF, pF, mF, F |
| Voltage | Units: V, mV, kV |
What each result means
- Stored energy = 0.5 × [Capacitance] × [Voltage]^2
- Charge = [Capacitance] × [Voltage]
Example values
How the main result changes when Voltage changes and everything else stays at the example values above:
| Voltage (V) | Stored energy (J) |
|---|---|
| 12.5 | 0.3672 |
| 18.75 | 0.8262 |
| 25 | 1.47 |
| 31.25 | 2.29 |
| 37.5 | 3.3 |
| 50 | 5.88 |
Formula
E = ½ C V²Q = C VWorked example
Inputs — Capacitance: 4,700 µF; Voltage: 25 V.
Results — Stored energy = 1.47 J; Charge = 0.1175 C.
Frequently asked questions
Why does voltage matter so much?
Energy rises with the square of voltage.
Is it safe to touch large capacitors?
No, they can hold a dangerous charge after power is removed.
What formula does the Capacitor Energy Calculator use?
E = ½ C V².
Can I work backwards from the result?
Yes. Type the result you want into Stored energy and the calculator finds the matching voltage.