Joules to Volts Calculator
Find voltage from energy and charge. Volts need both, so enter energy in joules and charge in coulombs (or milliamp-hours) to get V = J ÷ C.
Example: with Energy (joules) 12 · Charge 2 · Charge unit Coulombs (C) → Voltage: 6 V.
- Worked out12 J ÷ 2 C = 6 V
- FormulaV = J / C (joules per coulomb)
Computed by the calculator below using its default values. Change any input to see your own numbers.
Voltage is energy per unit charge: V = J ÷ C, rearranged from E = QV. You cannot get volts from joules alone — the charge that moved is required.
Why volts need charge
A joule is energy; a volt is energy per unit charge. Voltage answers the question 'how much energy does each coulomb of charge carry?' — so it is defined as V = J ÷ C. That is why a joules figure alone cannot give you volts: you also need to know how much charge moved to release or store that energy.
The relationship comes straight from E = QV, the energy stored or delivered when charge Q crosses a potential difference V. Rearranged, V = E ÷ Q. If your charge is given in milliamp-hours, as battery capacities usually are, convert first: one mAh equals 3.6 coulombs, because a milliamp for an hour is 0.001 A × 3,600 s.
How it’s calculated
V = J ÷ C, rearranged from the energy relation E = QV. Charge entered in milliamp-hours is converted at 1 mAh = 3.6 C before dividing (0.001 A × 3,600 s). Voltage is rounded to 6 significant decimals.
Assumes the full energy is delivered across a single, constant charge. Real batteries and capacitors deliver a voltage that changes as they discharge, so this is an average.
Joules and charge to volts
| Energy | Charge | Voltage |
|---|---|---|
| 12 J | 2 C | 6 V |
| 100 J | 5 C | 20 V |
| 9 J | 3 C | 3 V |
| 3,600 J | 1,000 C | 3.6 V |
| 36 J | 10 mAh | 1 V |
Computed with V = J ÷ C; 1 mAh = 3.6 C.
Common mistakes
- Trying to get volts from joules alone — the charge that moved is required.
- Mixing mAh and coulombs: 1 mAh is 3.6 C, not 1 C.
- Confusing energy (joules) with power (watts); volts come from energy per charge, not from power.
Frequently asked questions
What is the joules to volts formula?
V = J ÷ C: volts equal joules of energy divided by coulombs of charge. It is the rearranged form of E = QV.
Can I convert joules to volts without charge?
No. Voltage is energy per unit charge, so you must know how many coulombs moved. Joules alone are not enough.
How do I use milliamp-hours here?
Convert mAh to coulombs first: multiply by 3.6. A 2,000 mAh charge is 7,200 C, then divide the energy by that.
What does 12 joules across 2 coulombs give?
12 ÷ 2 = 6 volts. Each coulomb carries 6 joules of energy.