kWh to joules
J = kWh × 3,600,000
Exact factor: 1 kWh = 1,000 W × 3,600 s.
Convert kWh to Joules (and Joules to kWh)
kWh to joules converter in both directions: exact factor (1 kWh = 3.6 MJ), formula, mental-math shortcut, conversion table and real examples (electric car battery, phone battery, a household's yearly use), including the difference between kW and kWh.
Conversion table
| kWh | J |
|---|---|
| 1 kWh | 3,600,000 J |
| 2 kWh | 7,200,000 J |
| 5 kWh | 18,000,000 J |
| 10 kWh | 36,000,000 J |
| 20 kWh | 72,000,000 J |
| 50 kWh | 180,000,000 J |
| 100 kWh | 360,000,000 J |
| 1,000 kWh | 3,600,000,000 J |
| J | kWh |
|---|---|
| 1 J | 0.0000002778 kWh |
| 2 J | 0.0000005556 kWh |
| 5 J | 0.000001389 kWh |
| 10 J | 0.000002778 kWh |
| 20 J | 0.000005556 kWh |
| 50 J | 0.00001389 kWh |
| 100 J | 0.00002778 kWh |
| 1,000 J | 0.0002778 kWh |
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How does this tool work?
This converter turns kilowatt-hours into joules and joules into kilowatt-hours: type a value in either field and the other updates at once. Use it to relate an electricity bill or a battery capacity to the SI unit of energy, to solve a physics problem, or to compare sources that use different units (megajoules from a gas supplier, kWh from an electricity meter).
The joule (J) is the SI unit of energy: the work done by a force of 1 newton over 1 metre, or 1 watt flowing for 1 second. The kilowatt-hour is the energy used by a power of 1 kW over 1 hour, that is 1,000 W × 3,600 s = 3,600,000 J. The factor 1 kWh = 3.6 MJ is therefore exact, with no rounding.
To go from kWh to joules, multiply by 3,600,000; to go from joules to kWh, divide by 3,600,000 (or multiply by the rounded 2.7778 × 10⁻⁷). Both fields stay in sync and the double arrow swaps the direction without losing the value you typed.
For a quick estimate, remember that 1 kWh is 3.6 MJ: multiply kWh by 3.6 to get megajoules, and MWh by 3.6 to get gigajoules. In reverse, 1 MJ ≈ 0.28 kWh, so 10 MJ ≈ 2.8 kWh.
Do not mix up kW and kWh. The kilowatt measures power (the rate of energy use at a given moment), the kilowatt-hour measures energy (power multiplied by time). A 2 kW heater running for 3 hours uses 6 kWh, or 21.6 MJ. Also keep the small calorie (1 cal = 4.184 J) apart from the food Calorie or kilocalorie (1 kcal = 4,184 J).
How to use this tool
Enter an amount of energy
In the Kilowatt-hours or the Joules field; decimals are accepted, and a value in watt-hours goes in as kWh once divided by 1,000.
Read the conversion
The other field updates on every keystroke; for large numbers, think in megajoules (1 MJ = 1,000,000 J) or gigajoules.
Swap if needed
The double arrow exchanges the two units; the table under the converter lists common correspondences to sanity-check an order of magnitude.
kWh to joules conversion formulas
The kilowatt-hour is defined exactly from the watt and the hour, hence from the joule.
Joules to kWh
kWh = J ÷ 3,600,000 ≈ J × 2.7778 × 10⁻⁷
The factor 2.7778 × 10⁻⁷ is rounded; the division is exact.
Energy of an appliance
E (kWh) = P (kW) × t (h)
Energy is power multiplied by time.
- J
- energy in joules (1 J = 1 W·s)
- kWh
- energy in kilowatt-hours (1 kWh = 3.6 MJ)
- P
- power in kilowatts
- t
- time in hours
Example: a 1.5 kW heater running for 4 h uses 6 kWh, which is 6 × 3,600,000 = 21,600,000 J (21.6 MJ).
Use cases
Bills and meters
Relate a consumption in kWh to figures given in megajoules or gigajoules, common for gas, district heating and energy reports.
Batteries and storage
Express the capacity of a car, e-bike or home battery in joules to compare it with other forms of energy.
Physics and engineering
Switch from kWh to joules in a homework problem, an efficiency calculation or a technical note that requires SI units.
Comparing energies
Compare orders of magnitude: kinetic energy, food energy (kcal), heat or fuel brought to a common unit.
Examples
One kilowatt-hour
1 kWh = 1,000 W × 3,600 s = 3,600,000 J, or 3.6 MJ.
Input
1 kWhResult
3,600,000 JElectric car battery
60 × 3,600,000 = 216,000,000 J, or 216 MJ stored in the pack.
Input
60 kWhResult
216,000,000 JSmartphone battery
0.015 × 3,600,000 = 54,000 J, or 54 kJ for a full charge.
Input
15 Wh = 0.015 kWhResult
54,000 JOne megajoule
1,000,000 ÷ 3,600,000 ≈ 0.2778 kWh, about 278 Wh.
Input
1,000,000 JResult
0.2778 kWhA home's yearly electricity use
10,500 × 3,600,000 = 37.8 × 10⁹ J, or 37.8 GJ per year (typical for a US household).
Input
10,500 kWhResult
37,800,000,000 JTips and best practices
- Quick reference: 1 kWh = 3.6 MJ and 1 MJ ≈ 0.28 kWh.
- kW is power, kWh is energy: kWh = kW × hours. A 1 kW appliance left on for 1 hour uses 1 kWh.
- 1 Wh = 3,600 J: for a battery rated in Wh, multiply by 3,600 to get joules.
- For food energy, 1 kcal = 4,184 J: 2,000 kcal ≈ 8.37 MJ ≈ 2.32 kWh.
- A watt is one joule per second: 100 W for 10 s is 1,000 J, but only 0.000278 kWh.
Sources and references
- BIPM, The International System of Units (SI Brochure) (opens in a new tab), Bureau international des poids et mesuresPage in English
- NIST, Guide for the Use of the International System of Units (SP 811), Appendix B.8: Factors for Units Listed Alphabetically (opens in a new tab)Page in English
Frequently asked questions
How many joules are in a kWh?
One kilowatt-hour is exactly 3,600,000 joules, or 3.6 megajoules. That is 1,000 watts for 3,600 seconds.
How do you convert kWh to joules?
Multiply the kWh by 3,600,000. For example, 2.5 kWh is 9,000,000 J, or 9 MJ.
How do you convert joules to kWh?
Divide the joules by 3,600,000. For example, 50,000,000 J is about 13.89 kWh, and 1,000,000 J is about 0.2778 kWh.
What is the difference between kW and kWh?
The kW measures instantaneous power, the kWh measures energy used over time. A 2 kW oven used for 1.5 hours consumes 2 × 1.5 = 3 kWh, or 10.8 MJ.
How many kWh are in a kilocalorie?
One kilocalorie is 4,184 J, about 0.001162 kWh (1.162 Wh). A 2,000 kcal day is roughly 2.32 kWh.
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