How to Convert Kilojoules to Watt-hours (kJ 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 kilojoules into watt-hours by hand, with examples and a quick-reference table.
The conversion
To convert kilojoules to watt-hours, multiply the value by 0.2777777778. To go the other way, divide by the same number (or multiply by 3.6). For a quick estimate, multiply by about 0.28.
Watt-hours = kilojoules × 0.2777777778
Worked examples
- 3 kJ = 0.833333 Wh
- 12.5 kJ = 3.4722 Wh
- 75 kJ = 20.8333 Wh
Kilojoules to Watt-hours table
| Kilojoules | Watt-hours |
|---|---|
| 1 kJ | 0.277778 Wh |
| 2 kJ | 0.555556 Wh |
| 5 kJ | 1.3889 Wh |
| 10 kJ | 2.7778 Wh |
| 20 kJ | 5.5556 Wh |
| 25 kJ | 6.9444 Wh |
| 50 kJ | 13.8889 Wh |
| 100 kJ | 27.7778 Wh |
| 250 kJ | 69.4444 Wh |
| 500 kJ | 138.8889 Wh |
| 1,000 kJ | 277.7778 Wh |
Common questions
Is kJ 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 Kilojoules 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.
Forgetting squared and cubed units
Area and volume factors are the length factor squared or cubed, so 1 m² is about 10.76 sq ft, not 3.28.
Mixing similar-sounding units
US and imperial gallons, pints and tons are different sizes, and decimal kilobytes differ from binary kibibytes.
Background
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.
Writing the units next to every number while you work is the simplest way to avoid mistakes. If the units do not cancel to leave the one you want, the calculation is set up wrongly.
For everyday use, three or four significant figures are usually enough. Engineering, science and trade documents may need more, and rounding should happen only at the end of a calculation.
For any value, use the Kilojoules to Watt-hours Converter or browse all energy converters.
Run your own numbers: Kilojoules to Watt-hours Converter