The joule is the SI derived unit of energy.
Joules to Watt-hours Converter — J to Wh
Convert Joule (J) to Watt-hour (Wh) using the exact conversion factor (1 joule = 0.0002777778 watt-hour). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Joules to Watt-hours 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.
A watt-hour is 3,600 joules.
Result = input x 1 / 3600.
Energy units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Joules to Watt-hours
Joule and Watt-hour 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. Joule is typically associated with standard scientific and engineering energy unit worldwide, while Watt-hour is typically associated with universal — standard consumer-electronics and battery energy unit worldwide.
Formula
watt-hours = joules × 0.000277777777778
This factor comes from each unit's defined relationship to the category's base unit: 1 joule equals 1 base unit, and 1 watt-hour equals 3600 base units, so dividing one by the other gives the direct joule-to-watt-hour factor of 0.000277777777778.
Simple example
1 J × 0.0002777777778 = 0.0002777778 Wh
1 joule = 0.0002777778 watt-hours.
Real-world example
100 J × 0.0002777777778 = 0.0277777778 Wh
100 joules = 0.0277777778 watt-hours.
Conversion table
| Joule (J) | Watt-hour (Wh) |
|---|---|
| 1 J | 0.0002777778 Wh |
| 10 J | 0.0027777778 Wh |
| 50 J | 0.0138888889 Wh |
| 100 J | 0.0277777778 Wh |
| 500 J | 0.1388888889 Wh |
| 1,000 J | 0.2777777778 Wh |
Reverse conversion: Watt-hour to Joule
0.0002777778 Wh × 3600 = 1.00000008 J
0.0002777778 watt-hours = 1.00000008 joules.
joules = watt-hours × 3600
For a page dedicated to this direction, see Watt-hour to Joule.
Joule vs. Watt-hour
| Aspect | Joule | Watt-hour |
|---|---|---|
| Family | SI derived unit | metric derived energy unit |
| Typical use | Physics and engineering energy calculations | Phone, laptop, and power-bank battery capacity ratings |
| Where it's used | Standard scientific and engineering energy unit worldwide | Universal — standard consumer-electronics and battery energy unit worldwide |
Understanding the Joule
Joule (J) measures energy. The joule is the SI derived unit of energy, defined as the work done by one newton acting over one meter. It is classified as a SI derived unit.
Where it's used: Standard scientific and engineering energy unit worldwide
Uses of the Joule today
- Physics and engineering energy calculations
- Electrical energy in scientific contexts (though kWh is used for billing)
- Nutrition labeling in some countries (alongside or instead of calories)
History of the Joule
The joule is named after English physicist James Prescott Joule, whose experiments in the 1840s established the mechanical equivalent of heat — demonstrating that mechanical work and heat are interchangeable forms of energy, foundational to the first law of thermodynamics.
The unit itself was formally adopted as the SI derived unit of energy by international agreement as part of the broader SI system, defined coherently from the base units (kg, m, s) rather than as an independent physical standard.
Historical origin. Joule was not the invention of a single named person; it developed through the process described above.
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
Joule — sources
- BIPM SI Brochure — Coherent derived units — Defines the joule as the SI unit of energy.
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 joule?
1 joule equals 0.0002777778 watt-hours, using the exact defined conversion factor rather than an estimate.
How do I convert joule to watt-hour?
Multiply the joule value by 0.0002777777778. The converter above does this instantly to whatever precision you set.
How do I convert watt-hour back to joule?
Use the reverse factor: 1 watt-hour equals 3,600 joules. You can also use the swap control in the converter above to flip the direction instantly.
What is a joule?
Joule (J) measures energy. The joule is the SI derived unit of energy, defined as the work done by one newton acting over one meter. It is classified as a SI derived unit.
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 joule to watt-hour conversion exact?
Yes. Both joule and watt-hour are defined by fixed standards rather than physical artifacts, so the factor of 0.0002777777778 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 joule still used today?
Standard scientific and engineering energy unit worldwide