Volts to Joules Converter
Moving 5 coulombs of charge through 12 volts takes 60 joules of energy.
Quick answer: Multiply the volts by the charge in coulombs. For example, 12 V and 5 C is 60 J, 230 V and 100 C is 23,000 J and 3.7 V and 3,600 C is 13,320 J.
The volts to joules formula
Energy in joules equals voltage in volts times charge in coulombs. One volt is one joule of energy for each coulomb of charge (Wikipedia: Volt).
You need the charge as well as the voltage. Volts alone do not give an amount of energy.
Take 12 V and 5 C. 12 × 5 gives 60 J.
Take 230 V and 100 C. 230 × 100 gives 23,000 J.
Energy moved by a charge
The formula works for a battery, a capacitor discharge or any charge that moves through a voltage difference.
If the voltage changes during the move, use the average voltage.
How to convert volts to joules step by step
- Enter the voltage in volts.
- Enter the charge in coulombs.
- Read the energy in joules.
- See the last column for the same energy in watt-hours.
Example 1: 12 V and 5 C
- Start with 12 V and 5 C.
- 12 × 5 = 60.
- The energy is 60 J.
12 V and 5 C = 60 J
Example 2: 230 V and 100 C
- Start with 230 V and 100 C.
- 230 × 100 = 23,000.
- The energy is 23,000 J.
230 V and 100 C = 23,000 J
Example 3: 3.7 V and 3,600 C
- Start with 3.7 V and 3,600 C.
- 3.7 × 3,600 = 13,320.
- The energy is 13,320 J.
3.7 V and 3,600 C = 13,320 J
To get the charge from amps and seconds, multiply the amps by the time (Wikipedia: Ampere).
volts to joules conversion table
| Case | Energy | In Wh |
|---|---|---|
| 1.5 V and 1 C | 1.5 J | 0.000417 Wh |
| 3.7 V and 10 C | 37 J | 0.0103 Wh |
| 5 V and 100 C | 500 J | 0.1389 Wh |
| 9 V and 50 C | 450 J | 0.125 Wh |
| 12 V and 5 C | 60 J | 0.0167 Wh |
| 12 V and 100 C | 1,200 J | 0.3333 Wh |
| 12 V and 3,600 C | 43,200 J | 12 Wh |
| 24 V and 500 C | 12,000 J | 3.333 Wh |
| 120 V and 1,000 C | 120,000 J | 33.333 Wh |
| 230 V and 100 C | 23,000 J | 6.389 Wh |
| 230 V and 3,600 C | 828,000 J | 230 Wh |
The highlighted row is the default of the calculator. The last column gives Wh.
A quick mental shortcut for volts to joules
One coulomb through one volt is one joule.
One watt-hour is 3,600 joules.
What a volt means
One volt gives one joule of energy to each coulomb that passes through it (Wikipedia: Volt).
So the voltage is the energy per unit of charge.
Joules and watt-hours
One watt-hour is 3,600 joules, because one watt is one joule per second and an hour has 3,600 seconds.
So 43,200 J from a 12 V battery that moves 3,600 C equals 12 Wh.
Using amp-hours
One amp-hour is 3,600 coulombs (Wikipedia: Ampere-hour).
A 12 V battery with 1 Ah then holds 43,200 J, or 12 Wh.
Charge from current
Charge equals current times time. A current of 2 A for 30 s moves 60 C.
At 12 V, that charge carries 720 J.
A small battery example
A 3.7 V cell that delivers 3,600 C gives 13,320 J, which is 3.7 Wh.
That is the same as a 1 Ah cell at 3.7 V.
Going the other way
To get the charge, divide the energy by the volts.
For 60 J at 12 V, the charge is 5 C.
Check your answer
Divide your joules by the volts. You should get the coulombs back.
For 60 J at 12 V the result is 5 C, which matches.
Capacitors are different
A capacitor stores half of charge times voltage, because its voltage falls as it discharges. A 1 F capacitor at 5 V holds 12.5 J, not 25 J.
The simple V times Q rule fits a charge that moves through a steady voltage, such as a battery.
From energy to power
One joule is one watt for one second (Wikipedia: Watt). If 60 J moves in 2 seconds, the power is 30 W.
A quick unit check
Volts times coulombs gives joules, because a volt is a joule per coulomb. If the units do not cancel this way, recheck your inputs.
A small cell example
A 1.5 V cell that moves 2,000 C delivers 3,000 J. That is about 0.83333 Wh.
Joules and kilowatt-hours
One kilowatt-hour is 3,600,000 joules. So small amounts of energy in joules are tiny next to a household unit.
Quick conversion answers
| Conversion | Result |
|---|---|
| 1.5 V and 2 C | 3 J |
| 5 V and 20 C | 100 J |
| 12 V and 60 C | 720 J |
| 24 V and 120 C | 2,880 J |
| 120 V and 300 C | 36,000 J |
| 230 V and 1,000 C | 230,000 J |
Where this conversion is used
Students learn the link between voltage, charge and energy.
Hobbyists estimate how much energy a battery can deliver.
Engineers size the energy in capacitor discharges.
Common mistakes to avoid
- Using amps instead of coulombs. Multiply the amps by the seconds first to get the charge.
- Mixing joules and watt-hours. One watt-hour is 3,600 joules.
- Ignoring voltage drop. A falling voltage means the average is lower than the start value.
- Treating volts as energy. Volts are energy per coulomb.
Related converters
Frequently asked questions
Can I convert volts to joules directly?
No. You also need the charge in coulombs.
What is the formula?
Energy in joules equals volts times coulombs.
How many joules is 12 V and 5 C?
It is 60 J.
How many joules is a watt-hour?
One watt-hour is 3,600 joules.
How do I get coulombs from amps?
Multiply the amps by the time in seconds.
What if the voltage changes?
Use the average voltage over the move.
Sources
- Wikipedia: Volt (en.wikipedia.org)
- Wikipedia: Ampere-hour (en.wikipedia.org)
- Wikipedia: Coulomb (en.wikipedia.org)
