Watt Hours to Megajoules
Type a value in either box to convert between watt hours and megajoules. The factor is 0.0036.
| Watt Hours | Megajoules |
|---|---|
| 1 Wh | 0.0036 MJ |
| 2 Wh | 0.0072 MJ |
| 3 Wh | 0.0108 MJ |
| 5 Wh | 0.018 MJ |
| 10 Wh | 0.036 MJ |
| 25 Wh | 0.09 MJ |
| 50 Wh | 0.18 MJ |
| 100 Wh | 0.36 MJ |
How to use
- Enter a value in the Watt Hours field.
- The Megajoules figure appears immediately — no button to press.
- Typing in the Megajoules field converts back to Watt Hours the same way.
- Use the reference table for the values that come up most often.
Watt Hours to Megajoules formula
To convert watt hours to megajoules, multiply by 0.0036.
MJ = Wh × 0.0036
Why this factor: the watt-hour and the megajoule are both defined against the joule, so dividing one definition by the other gives 0.0036 directly. Both definitions are set out in full below.
To go the other way, divide by 0.0036 — or use the Megajoules to Watt Hours converter, which is the same calculation reversed.
Worked example
Take 2000 Wh and multiply by the factor 0.0036: the result is 7.2 MJ.
2000 Wh × 0.0036 = 7.2 MJ
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 megajoule?
A megajoule is one million joules, used for substantial energy quantities.
Definition: Exactly 1×10⁶ joules. One kilowatt-hour is exactly 3.6 MJ.
Where it is used: Fuel energy content, natural gas billing, and industrial energy accounting.
Watt Hours vs Megajoules
The watt-hour is a specialized unit while the megajoule 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 megajoules are in a watt-hour?
One watt-hour equals 0.0036 megajoules.
What is the formula to convert watt hours to megajoules?
Multiply the number of watt hours by 0.0036. To reverse it, divide by 0.0036 instead.
How do I convert megajoules back to watt hours?
Divide by 0.0036, which is the same as multiplying by 277.777778.
How many megajoules are in 10 watt hours?
10 Wh works out to 0.036 MJ.
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.