Millijoule is 0.001 joule units.
Millijoules to Watt-hours Converter — mJ to Wh
Convert Millijoule (mJ) to Watt-hour (Wh) using the exact conversion factor (1 millijoule = 2.777778e-7 watt-hour). See the formula, worked examples, conversion table, and common uses.
Millijoules to Watt-hours converter
Converter
Energy Converter
Convert joules, calories, kilowatt-hours, BTU, electronvolts, therms, and mechanical work units.
Context values
Some unit families need one extra value for a physically accurate result.
A watt-hour is 3,600 joules.
Result = input x 0.001 / 3600.
Energy uses the joule as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Millijoules to Watt-hours
Millijoule and Watt-hour both measure energy, and the conversion is especially useful for comparing nutrition labels (kilocalories) against scientific energy figures (joules). Specifically: Millijoule is 0.001 joule units, and a watt-hour is 3,600 joules.
Formula
watt-hours = millijoules × 2.777778e-7
This factor comes from each unit's defined relationship to the category's base unit: 1 millijoule equals 0.001 base units, and 1 watt-hour equals 3600 base units, so dividing one by the other gives the direct millijoule-to-watt-hour factor of 2.777778e-7.
Simple example
1 mJ × 2.777778e-7 = 2.777778e-7 Wh
1 millijoule = 2.777778e-7 watt-hours.
Real-world example
100 mJ × 2.777778e-7 = 0.0000277778 Wh
100 millijoules = 0.0000277778 watt-hours.
Conversion table
| Millijoule (mJ) | Watt-hour (Wh) |
|---|---|
| 1 mJ | 2.777778e-7 Wh |
| 10 mJ | 0.0000027778 Wh |
| 100 mJ | 0.0000277778 Wh |
| 500 mJ | 0.0001388889 Wh |
| 1,000 mJ | 0.0002777778 Wh |
| 2,000 mJ | 0.0005555556 Wh |
Reverse conversion: Watt-hour to Millijoule
2.777778e-7 Wh × 3600000 = 1.00000008 mJ
2.777778e-7 watt-hours = 1.00000008 millijoules.
millijoules = watt-hours × 3600000
For a page dedicated to this direction, see Watt-hour to Millijoule.
Understanding the Millijoule (mJ)
Millijoule is 0.001 joule units.
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
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 watt-hours are in 1 millijoule?
1 millijoule equals 2.777778e-7 watt-hours, using the exact defined conversion factor rather than an estimate.
How do I convert millijoule to watt-hour?
Multiply the millijoule value by 2.777778e-7. The converter above does this instantly to whatever precision you set.
How do I convert watt-hour back to millijoule?
Use the reverse factor: 1 watt-hour equals 3,600,000 millijoules. You can also use the swap control in the converter above to flip the direction instantly.
What is a millijoule?
Millijoule (mJ) is a unit of energy.
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.
Is the millijoule to watt-hour conversion exact?
Yes. Both millijoule and watt-hour are defined by fixed standards rather than physical artifacts, so the factor of 2.777778e-7 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.