Joules to kWh Converter
Convert joules (J) to kilowatt-hours (kWh) and back
Quick answer
One kilowatt-hour equals 3,600,000 joules. To convert joules to kWh, divide by 3,600,000; to convert kWh to joules, multiply by 3,600,000. For watt-hours, divide joules by 3,600.
Unfamiliar with a term? Check the electric motor glossary.
| Joules (J) | Kilowatt-hours (kWh) |
|---|---|
| 1000000 | 0.2778 |
| 2000000 | 0.5556 |
| 3000000 | 0.8333 |
| 4000000 | 1.1111 |
| 5000000 | 1.3889 |
| 6000000 | 1.6667 |
| 7000000 | 1.9444 |
| 8000000 | 2.2222 |
| 9000000 | 2.5000 |
| 10000000 | 2.7778 |
Energy Conversion Chart
Formula
kWh = J ÷ 3,600,000
J = kWh × 3,600,000
Wh = J ÷ 3,600
The factor comes straight from the definitions: a joule is one watt-second, and one kilowatt-hour is 1,000 W for 3,600 s, which is 3,600,000 W·s or 3,600,000 J (3.6 MJ).
Table of Common Energies
| Energy | Joules (J) | Watt-hours (Wh) | Kilowatt-hours (kWh) |
|---|---|---|---|
| 1 J | 1 | 0.000278 | 2.78 × 10−7 |
| 1 kJ | 1,000 | 0.278 | 0.000278 |
| 1 kcal (food calorie) | 4,184 | 1.162 | 0.001162 |
| 1 Wh | 3,600 | 1 | 0.001 |
| 1 MJ | 1,000,000 | 277.8 | 0.2778 |
| 1 kWh | 3,600,000 | 1,000 | 1 |
| 10 kWh | 36,000,000 | 10,000 | 10 |
Worked Examples
- A motor running for two hours. A motor drawing 500 W for 2 h uses 500 W × 7,200 s = 3,600,000 J. 3,600,000 ÷ 3,600,000 = 1 kWh.
- A drone battery. A 6S pack of 10 Ah at 22.2 V nominal stores 222 Wh. 222 × 3,600 = 799,200 J ≈ 0.8 MJ = 0.222 kWh.
- Heat in a robot joint. A motor losing 15 W as heat over a 10-minute cycle turns 15 W × 600 s = 9,000 J into heat. 9,000 ÷ 3,600,000 = 0.0025 kWh, or 2.5 Wh.
Why Engineers Use Both Units
Joules are the natural unit for the energy a motor or actuator uses in one move or one cycle, and for losses: heat in a winding, energy in a braking pulse, kinetic energy in a rotor. Kilowatt-hours are the unit on electricity bills and battery datasheets (battery packs are usually rated in Wh). When you size a battery for a motor, you typically work out energy per cycle in joules from the duty cycle, multiply by the number of cycles, and convert to Wh or kWh to choose the pack. Efficiency enters at that step: the battery has to supply the mechanical energy divided by the drive and motor efficiency.
Where the Units Come From
The joule is the SI unit of energy, named after James Prescott Joule, whose experiments in the 1840s tied mechanical work to heat; one joule is the work done by a force of one newton over one metre. The watt-hour, and with it the kilowatt-hour, grew out of electricity metering: it is power in watts, named after James Watt, multiplied by time in hours, which is how utilities measured and billed energy from the start.
Frequently Asked Questions
What is 1 kWh in joules?
1 kWh equals 3,600,000 J, or 3.6 MJ.
How do I convert joules to kWh?
Divide the number of joules by 3,600,000. For example, 7,200,000 J ÷ 3,600,000 = 2 kWh.
How do I convert kWh to joules?
Multiply by 3,600,000. For example, 0.5 kWh × 3,600,000 = 1,800,000 J.
How do I convert joules to watt-hours?
Divide by 3,600. For example, 7,200 J is 2 Wh.
Is a joule the same as a watt-second?
Yes. One joule equals one watt-second, which is why 1 kWh = 1,000 W × 3,600 s = 3,600,000 J.
Why is the conversion factor so large?
A kilowatt-hour is a large amount of energy: one kilowatt for a whole hour. A joule is one watt for one second, so there are 3.6 million joules in a kilowatt-hour.