Capacitor Energy and Charge Calculator
By Santaji GadepatilinUpdated October 27, 2026
A capacitor stores energy in the electric field between its plates, and the amount rises with the square of the voltage. Read about the capacitor working principle and how supercapacitors store far more. This free capacitor energy and charge calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the capacitor energy and charge calculator
Enter the capacitance and the voltage. The calculator gives the stored energy and the charge. Press × on Voltage to find the voltage needed to store a given energy.
For more background, read Capacitor Types Explained and How to Test a Capacitor.
Capacitor energy and charge formulas
E = ½ × C × V² · Q = C × V
Stored energy examples
| Capacitor | Voltage | Energy |
|---|---|---|
| 100 µF electrolytic | 25 V | 0.031 J |
| 1,000 µF electrolytic | 50 V | 1.25 J |
| 4,700 µF DC bus | 400 V | 376 J |
| Camera flash, 200 µF | 330 V | 10.9 J |
| Supercapacitor 10 F | 2.7 V | 36.5 J |
| Supercapacitor 3,000 F | 2.7 V | 10,935 J (3.04 Wh) |
Supercapacitors vs batteries
A 3,000 F, 2.7 V supercapacitor stores about 3 Wh — roughly what a few AA batteries hold — but can deliver it in seconds and survive hundreds of thousands of cycles. They suit short backup, regenerative braking and burst power.
Safety
Energy above about 0.25 J at voltages over 50 V can give a dangerous shock. Discharge large capacitors through a suitable resistor (not a screwdriver), then confirm 0 V with a meter.
Series and parallel
- Parallel: C = C₁ + C₂ (same voltage rating).
- Series: 1/C = 1/C₁ + 1/C₂ — higher voltage, lower capacitance; use balancing resistors.
Frequently asked questions
How much energy does a capacitor store?
E = ½ × C × V². A 1,000 µF capacitor at 50 V stores 1.25 J.
How much usable energy is there between two voltages?
E = ½ C (V₁² − V₂²). A supercapacitor discharged from full voltage to half voltage delivers 75% of its stored energy.
Why are charged capacitors dangerous?
Large capacitors in power supplies, VFDs and microwave ovens can hold lethal energy for minutes after switch-off. Always discharge and verify with a meter before working.
What is the charge on a capacitor?
Q = C × V, in coulombs.