Capacitor Energy Calculator
E = ½ C V². 4700 µF at 50 V stores 5.875 J.
Calculator
Formula
Stored energy
E = ½ C V² Charge
Q = C V Variables
| Symbol | Meaning | Unit | Typical range | Precision | Default |
|---|---|---|---|---|---|
| C | Capacitance | F | ≥ 0 pF | 4 sig | 4.7 mF |
| V | Voltage | V | — | 4 sig | 50 V |
| R | Resistance (optional τ) | Ω | — | 4 sig | |
| E | Stored energy | J | — | 4 sig | — |
| EWh | Stored energy | Wh | — | 4 sig | — |
| Q | Charge | — | — | 4 sig | — |
Worked example
4700 µF at 50 V
| Input | Value |
|---|---|
| C · Capacitance | 4.7 mF |
| V · Voltage | 50 V |
| Output | Value |
|---|---|
| E · Stored energy | 5.875 J |
| EWh · Stored energy | 0.001632 Wh |
| Q · Charge | 0.235 |
100 µF at 5 V
| Input | Value |
|---|---|
| C · Capacitance | 100 µF |
| V · Voltage | 5 V |
| Output | Value |
|---|---|
| E · Stored energy | 1.25 mJ |
| Q · Charge | 0.0005 |
How it works
The energy in a capacitor is the thing you feel when a bulk cap dumps into a screwdriver. It is also the number you need before you pick a bleeder.
Enter C and V. Optional R adds the time constant. For a full 1τ–5τ table, open the RC time constant calculator; for a safety dump toward a labelled Vsafe, open the discharge calculator.
Pitfalls
- Forgetting that energy scales with V² — 2× voltage is 4× energy.
- Reading a millijoule figure as joules when comparing to a dump resistor.
- This is stored energy, not a battery watt-hour rating.
FAQ
How much energy in 4700 µF at 50 V?
½ × 0.0047 × 50² = 5.875 J.
Why does negative voltage still show energy?
E uses V². The sign sits on the charge Q = C V.
Can I also get τ?
Yes. Optional R reports τ = R C from the same engine.
Is Wh useful here?
Only as a unit conversion. These energies are small compared with a cell.
Related
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