Watt Hours to Kilojoules
An instant watt hours-to-kilojoules converter, with the formula and a reference table below.
| Watt Hours | Kilojoules |
|---|---|
| 1 Wh | 3.6 kJ |
| 2 Wh | 7.2 kJ |
| 3 Wh | 10.8 kJ |
| 5 Wh | 18 kJ |
| 10 Wh | 36 kJ |
| 25 Wh | 90 kJ |
| 50 Wh | 180 kJ |
| 100 Wh | 360 kJ |
How to use
- Enter a value in the Watt Hours field.
- The Kilojoules figure appears immediately — no button to press.
- Typing in the Kilojoules field converts back to Watt Hours the same way.
- Use the reference table for the values that come up most often.
Watt Hours to Kilojoules formula
To convert watt hours to kilojoules, multiply by 3.6.
kJ = Wh × 3.6
Put another way, one watt-hour is exactly 18/5 kilojoules.
Why this factor: the watt-hour and the kilojoule are both defined against the joule, so dividing one definition by the other gives 3.6 directly. Both definitions are set out in full below.
To go the other way, divide by 3.6 — or use the Kilojoules to Watt Hours converter, which is the same calculation reversed.
Worked example
Given 2000 Wh, multiplying by 3.6 yields 7200 kJ.
2000 Wh × 3.6 = 7200 kJ
The converter above does this for any value you type, in either direction.
What is a watt-hour?
A watt-hour is the energy delivered by one watt of power sustained for one hour.
Definition: Exactly 3,600 joules.
Where it is used: Battery capacity for laptops, e-bikes and power tools, and small-scale energy metering.
Worth knowing: Airline lithium-battery limits are set in watt-hours, which is why laptop and power-bank capacities are labelled in Wh.
What is a kilojoule?
A kilojoule is 1,000 joules, the metric unit of food energy.
Definition: Exactly 1,000 joules.
Where it is used: Nutrition labels in Europe and Australia, and heating and cooling loads.
Watt Hours vs Kilojoules
The watt-hour is a specialized unit while the kilojoule is a metric unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many kilojoules are in a watt-hour?
One watt-hour equals 3.6 kilojoules.
What is the formula to convert watt hours to kilojoules?
Multiply the number of watt hours by 3.6. To reverse it, divide by 3.6 instead.
How do I convert kilojoules back to watt hours?
Divide by 3.6, which is the same as multiplying by 0.277777778.
How many kilojoules are in 10 watt hours?
10 Wh works out to 36 kJ.
Is there anything to watch out for with watt hours?
Airline lithium-battery limits are set in watt-hours, which is why laptop and power-bank capacities are labelled in Wh.
How is the watt-hour defined?
Exactly 3,600 joules.