How to Convert Joules to Watt-hours (J to Wh)
Energy conversions link food labels in kJ and kcal, SP Group bills in kWh and air-conditioner capacity in BTU. This guide shows how to convert joules into watt-hours by hand, with examples and a quick-reference table.
The conversion
To convert joules to watt-hours, multiply the value by 0.0002777778. To go the other way, divide by the same number (or multiply by 3,600). Because the factor is tiny, scientific notation keeps the numbers manageable.
Watt-hours = joules × 0.0002777778
Worked examples
- 3 J = 0.000833 Wh
- 12.5 J = 0.003472 Wh
- 75 J = 0.020833 Wh
Joules to Watt-hours table
| Joules | Watt-hours |
|---|---|
| 1 J | 0.000278 Wh |
| 2 J | 0.000556 Wh |
| 5 J | 0.001389 Wh |
| 10 J | 0.002778 Wh |
| 20 J | 0.005556 Wh |
| 25 J | 0.006944 Wh |
| 50 J | 0.013889 Wh |
| 100 J | 0.027778 Wh |
| 250 J | 0.069444 Wh |
| 500 J | 0.138889 Wh |
| 1,000 J | 0.277778 Wh |
Common questions
Is J to Wh exact?
The factors used here are the internationally defined values where they exist; results are rounded for display only.
How do I convert back?
Use the Watt-hours to Joules converter.
Mistakes to avoid
Rounding the factor too early
Using 3 instead of 3.28 for feet per metre introduces an error of almost 9% before you have started.
Mixing similar-sounding units
US and imperial gallons, pints and tons are different sizes, and decimal kilobytes differ from binary kibibytes.
Multiplying when you should divide
Converting to a smaller unit gives a bigger number, and converting to a larger unit gives a smaller one. If your answer moves the wrong way, you have inverted the factor.
Background
Unit conversion is simply multiplication by a fixed ratio. The ratio between two units of the same quantity never changes, so once you know it you can convert any value in either direction.
Singapore adopted the metric system in the 1970s, replacing imperial units and traditional Chinese measures in most official uses. Metric units are now standard in schools, trade and government, but older units survive in property, markets and imported goods.
A conversion table is handy for common values, but a calculator is faster and avoids interpolation errors for anything in between.
For any value, use the Joules to Watt-hours Converter or browse all energy converters.
Run your own numbers: Joules to Watt-hours Converter