| Capacitor | Capacitance | Typical use |
|---|---|---|
| Ceramic (small) | 1 pF – 1 µF | Filtering, decoupling, RF |
| Film | 1 nF – 10 µF | Audio, timing circuits |
| Electrolytic | 1 µF – 10,000 µF | Power supply smoothing |
| Supercapacitor | 0.1 F – 3,000 F | Energy storage, backup power |
| Photoflash | 100 µF – 1,200 µF | Camera flash, energy discharge |
Joules (J) measure energy, while volts (V) measure electric potential. You cannot convert one directly into the other without a third quantity, because they describe different physical properties. For a capacitor, that linking quantity is capacitance (measured in farads, F).
A charged capacitor stores energy according to the formula E = ½ · C · V². Rearranging this equation lets you find the voltage when you know the stored energy and the capacitance:
V = √(2J / C) — divide twice the energy by the capacitance, then take the square root. The result is the voltage across the capacitor.
J = ½ · C · V² — multiply half the capacitance by the square of the voltage to get the stored energy in joules.
This calculator runs both directions live as you type. Pick the capacitance unit (farads, millifarads, microfarads, nanofarads, or picofarads) that matches your component and the tool handles the conversion automatically. Everything is computed in your browser — nothing is uploaded to a server, so it works offline and stays private.
These relationships are used constantly in electronics design: sizing capacitors for camera flashes, defibrillators, power supplies, supercapacitor banks, and energy-discharge circuits all rely on the energy-voltage relationship shown above.
Not directly. Joules measure energy and volts measure potential. You need capacitance as the link. With the energy stored in a capacitor and its capacitance, you can find the voltage using V = √(2J / C).
V = √(2J / C), where J is energy in joules and C is capacitance in farads. The result is voltage in volts.
Energy stored in a capacitor depends on both voltage and capacitance (E = ½CV²). Without knowing the capacitance, voltage cannot be determined from energy alone.
You can enter capacitance in farads (F), millifarads (mF), microfarads (µF), nanofarads (nF), or picofarads (pF). The calculator converts to farads internally before computing.
Yes. It is completely free, requires no signup, and runs entirely in your browser. No data is sent to any server.