Capacitor Charge Calculator
Two Numbers Every Capacitor Spec Sheet Implies
A capacitor's rating — say, 100µF at a 12V working voltage — doesn't directly state how much electrical charge it can hold or how much energy it stores when fully charged, even though both follow immediately from the capacitance and voltage. This calculator computes both: the charge in coulombs, which determines how much current the capacitor can briefly supply, and the energy in joules, which determines how much work it can do.
The Formula
Charge and energy stored in a capacitor are standard results from its capacitance and voltage:
Energy: E = ½ × C × V²
Note that energy scales with the square of voltage, not linearly — doubling the voltage across a capacitor quadruples the energy it stores, even though the charge only doubles.
Where This Calculation Matters
- Power supply and filter design — sizing a smoothing or decoupling capacitor to hold enough charge to ride through brief voltage dips.
- Flash and pulse circuits — calculating the energy a capacitor can deliver in a single discharge, relevant to camera flashes, defibrillators, and pulsed lasers.
- Supercapacitor and energy storage applications — estimating usable energy storage for backup power or regenerative braking systems that use large-value capacitors instead of batteries.
- Safety assessment — a charged capacitor can retain a dangerous stored energy or charge even after power is removed, which is why some equipment specifies a discharge time before servicing.
Charge and Energy for Common Capacitor Values
| Capacitance | Voltage | Charge (Q) | Energy (E) |
|---|---|---|---|
| 10 µF | 9 V | 90.0 µC | 405.0 µJ |
| 100 µF | 12 V | 1.2 mC | 7.2 mJ |
| 1000 µF | 5 V | 5.0 mC | 12.5 mJ |
| 1 F (supercapacitor) | 5 V | 5.0 C | 12.5 J |
A 1-farad supercapacitor stores orders of magnitude more charge and energy than a typical microfarad-range electrolytic capacitor — which is why supercapacitors are used for short-term energy backup rather than filtering.
How to Use This Calculator
- Enter the Capacitance value and choose its unit (pF, nF, µF, mF, or F).
- Enter the Voltage (V) across the capacitor.
- Select Calculate to see the stored charge and energy, automatically scaled to a readable unit.
Related Calculations
Decoding the resistor sitting next to that capacitor on a circuit? Use the Resistor Color Code Calculator. Estimating runtime for a battery-powered circuit instead? See the Battery Life Calculator.