A watt-hour is 3,600 joules.
Watt-hours to Millijoules Converter — Wh to mJ
Convert Watt-hour (Wh) to Millijoule (mJ) using the exact conversion factor (1 watt-hour = 3,600,000 millijoule). See the formula, worked examples, conversion table, and common uses.
Watt-hours to Millijoules converter
Converter
Engineering Converter
Convert common stress, force, torque, power, and energy units used in engineering.
Context values
Some unit families need one extra value for a physically accurate result.
Millijoule is 0.001 joule units.
Result = input x 3600 / 0.001.
Energy units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Watt-hours to Millijoules
Watt-hour and Millijoule both measure a quantity used in structural or mechanical engineering — commonly stress, pressure, force, torque, power, or energy — where converting between the unit conventions used in different regions, industries, or equipment specifications is a routine part of design work. Watt-hour is most often used for phone, laptop, and power-bank battery capacity ratings.
Formula
millijoules = watt-hours × 3600000
This factor comes from each unit's defined relationship to the category's base unit: 1 watt-hour equals 3600 base units, and 1 millijoule equals 0.001 base units, so dividing one by the other gives the direct watt-hour-to-millijoule factor of 3600000.
Simple example
1 Wh × 3600000 = 3,600,000 mJ
1 watt-hour = 3,600,000 millijoules.
Real-world example
100 Wh × 3600000 = 360,000,000 mJ
100 watt-hours = 360,000,000 millijoules.
Conversion table
| Watt-hour (Wh) | Millijoule (mJ) |
|---|---|
| 1 Wh | 3,600,000 mJ |
| 10 Wh | 36,000,000 mJ |
| 50 Wh | 180,000,000 mJ |
| 100 Wh | 360,000,000 mJ |
| 500 Wh | 1,800,000,000 mJ |
| 1,000 Wh | 3,600,000,000 mJ |
Reverse conversion: Millijoule to Watt-hour
1 mJ × 2.777778e-7 = 2.777778e-7 Wh
1 millijoule = 2.777778e-7 watt-hours.
watt-hours = millijoules × 2.777778e-7
For a page dedicated to this direction, see Millijoule to Watt-hour.
Understanding the Watt-hour
Watt-hour (Wh) measures energy. The energy delivered by one watt of power sustained for one hour — equal to 3,600 joules. It is classified as a metric derived energy unit.
Where it's used: Universal — standard consumer-electronics and battery energy unit worldwide
Wh vs. kWh. The same unit at different scales: 1,000 Wh equals 1 kWh. Wh suits small consumer-electronics batteries; kWh is used for household electricity billing and larger energy storage.
Uses of the Watt-hour today
- Phone, laptop, and power-bank battery capacity ratings
- Electric-vehicle battery capacity specifications
- Small-scale renewable energy (solar panel) output ratings
Understanding the Millijoule (mJ)
Millijoule is 0.001 joule units.
Watt-hour — sources
- BIPM SI Brochure — Watt-hour as a common energy unit derived from the coherent SI units watt and second (via the hour).
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many millijoules are in 1 watt-hour?
1 watt-hour equals 3,600,000 millijoules, using the exact defined conversion factor rather than an estimate.
How do I convert watt-hour to millijoule?
Multiply the watt-hour value by 3600000. The converter above does this instantly to whatever precision you set.
How do I convert millijoule back to watt-hour?
Use the reverse factor: 1 millijoule equals 2.777778e-7 watt-hours. You can also use the swap control in the converter above to flip the direction instantly.
What is a watt-hour?
Watt-hour (Wh) measures energy. The energy delivered by one watt of power sustained for one hour — equal to 3,600 joules. It is classified as a metric derived energy unit.
What is a millijoule?
Millijoule (mJ) is a unit of engineering.
Is the watt-hour to millijoule conversion exact?
Yes. Both watt-hour and millijoule are defined by fixed standards rather than physical artifacts, so the factor of 3600000 used above is exact to as many digits as you choose to display.
What is the difference between wh vs. kwh?
The same unit at different scales: 1,000 Wh equals 1 kWh. Wh suits small consumer-electronics batteries; kWh is used for household electricity billing and larger energy storage.
Where is the watt-hour still used today?
Universal — standard consumer-electronics and battery energy unit worldwide