Joules to Watt Hours
Convert joules (J) to watt hours (Wh). Both measure work and power, and the conversion comes up in nutrition, electricity, fitness work.
The Formula
``
watt hours = joules × 0.000277777777778
joules = watt hours × 3600
`
One joule is 2.7778e-4 watt hours, and one watt hour is 3,600 joules.
Conversion Table
| Joules | Watt Hours |
|---|---|
| 1 J | 2.7778e-4 Wh |
| 2 J | 5.5556e-4 Wh |
| 5 J | 0.001389 Wh |
| 10 J | 0.002778 Wh |
| 25 J | 0.006944 Wh |
| 50 J | 0.013889 Wh |
| 100 J | 0.027778 Wh |
| 500 J | 0.138889 Wh |
| 1,000 J | 0.277778 Wh |
The Other Direction
| Watt Hours | Joules |
|---|---|
| 1 Wh | 3,600 J |
| 2 Wh | 7,200 J |
| 5 Wh | 18,000 J |
| 10 Wh | 36,000 J |
| 25 Wh | 90,000 J |
| 50 Wh | 180,000 J |
| 100 Wh | 360,000 J |
| 500 Wh | 1,800,000 J |
| 1,000 Wh | 3,600,000 J |
What Each Unit Is
Joules (J) — the work done by one newton acting over one metre — the SI derived unit of energy. Named for James Prescott Joule, who established the mechanical equivalent of heat.
Watt Hours (Wh) — one watt sustained for one hour, or 3,600 joules. The practical electrical energy unit, following the adoption of the watt.
A Sense of Scale
Lifting an apple one metre takes about 1 J- A heartbeat uses roughly 1 J
- A phone battery holds 12–20 Wh
- A laptop battery is 50–100 Wh
Precision
The factor 0.000277777777778 is rounded. For engineering work carry more digits than the table above, and round only at the end — rounding at each step compounds.
In Code
`javascript
const jouleToWattHour = (value) => value * 0.000277777777778;
``
Where This Conversion Comes Up
- Nutrition
- Electricity
- Fitness
- Heating
- Fuel
How Many Decimals Do You Need?
Rounding the factor costs accuracy, and how much depends on the factor. Converting 137 J with the factor truncated at each decimal place:
| Decimals kept | Factor | 137 J becomes | Error |
|---|---|---|---|
| 0 | 0 | 0 | 100.0000% |
| 1 | 0 | 0 | 100.0000% |
| 2 | 0 | 0 | 100.0000% |
| 3 | 0 | 0 | 100.0000% |
| 4 | 0.0003 | 0.0411 | 8.0000% |
The right number of significant figures is set by your input, not by the converter. If you measured joules to three significant figures, the answer in watt hours is only good to three — writing more digits claims precision the measurement never had.