About the Joules to Volts Calculator
A volt is defined as one joule of energy per coulomb of charge, so converting joules to volts needs the charge as well as the energy. This calculator divides the energy in joules by the charge in coulombs and gives the potential difference in volts. It also shows how much energy a single electron gains when it moves through that voltage, in joules and in electronvolts, which links everyday electricity to the physics of particles. It is useful for physics homework, for working out the voltage in a charged capacitor and for checking battery and static discharge sums.
Updated October 2026
How to use the Joules to Volts Calculator
- 1Enter the energy in joules.
- 2Enter the charge in coulombs. One amp for one second is one coulomb.
- 3Read the voltage in volts.
- 4Look at the energy per electron in joules and electronvolts.
- 5Change the numbers to see how charge and energy change the voltage.
Examples
A static spark that releases 0.002 joules from 1 microcoulomb of charge corresponds to 2,000 volts. A small flash capacitor that dumps 100 joules from 0.1 coulombs sits at 1,000 volts. An electron accelerated through 10,000 volts gains 10,000 eV, or 1.6 × 10⁻¹⁵ joules.
For capacitor questions, remember that energy and voltage are not linked by charge alone. A capacitor of capacitance C charged to V volts stores half of C times V squared in joules, while the charge is C times V. So a 1,000 microfarad capacitor at 50 volts holds 1.25 joules and 0.05 coulombs. The ratio of those two, 25, is half the voltage, which shows why the simple joules-per-coulomb sum gives a different answer for a charging capacitor.
Terms worth knowing
- Joule: the SI unit of energy.
- Coulomb: the SI unit of electric charge.
- Volt: one joule per coulomb.
- Electronvolt: the energy of one electron through one volt.
- Capacitance: charge stored per volt, in farads.
Related physics and electrical tools
The Energy Converter changes between joules, calories and kilowatt-hours, the Ohm's Law Calculator links voltage with current and resistance, the Amps to Volts Calculator uses power or ohms, and the Joules to Watts Calculator finds power from energy and time.
Features
- Volts from joules and coulombs
- Energy per electron in J and eV
- Zero charge rejected clearly
- Works with very small and very large values
- Hints on turning mAh into coulombs
- Private and free
Frequently asked questions
What is the formula for joules to volts?
Volts equal joules divided by coulombs. If 60 joules of energy move 5 coulombs of charge, the voltage is 12 volts.
Can I convert joules to volts without the charge?
No. Energy alone does not set the voltage. The same 60 joules could be 12 volts at 5 coulombs or 6 volts at 10 coulombs, so you must know how much charge is involved.
How do I find coulombs from amps and seconds?
Multiply the current in amps by the time in seconds. A 2 amp current for 30 seconds moves 60 coulombs. A battery rated in mAh stores 3.6 coulombs per milliamp-hour, so a 1,000 mAh cell holds 3,600 coulombs.
What is an electronvolt?
An electronvolt (eV) is the energy gained by one electron crossing a potential difference of one volt, about 1.602 × 10⁻¹⁹ joules. It is the usual energy unit in atomic and particle physics.
How is this related to capacitors?
A charged capacitor stores energy E = ½CV². Together with the charge Q = CV, you can find the voltage from the stored energy and the capacitance. The simple joules-per-coulomb relation applies to any pair of points in a circuit.
Is it the same as converting joules to watts?
No. Joules measure energy and watts measure power, energy per second. The Joules to Watts Calculator converts between those, and this one links energy to voltage via charge.