How to Convert Watt-hours to Kilojoules (Wh to kJ)
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 watt-hours into kilojoules by hand, with examples and a quick-reference table.
The conversion
To convert watt-hours to kilojoules, multiply the value by 3.6. To go the other way, divide by the same number (or multiply by 0.2777777778). For a quick estimate, multiply by about 3.6.
Kilojoules = watt-hours × 3.6
Worked examples
- 3 Wh = 10.8 kJ
- 12.5 Wh = 45 kJ
- 75 Wh = 270 kJ
Watt-hours to Kilojoules table
| Watt-hours | Kilojoules |
|---|---|
| 1 Wh | 3.6 kJ |
| 2 Wh | 7.2 kJ |
| 5 Wh | 18 kJ |
| 10 Wh | 36 kJ |
| 20 Wh | 72 kJ |
| 25 Wh | 90 kJ |
| 50 Wh | 180 kJ |
| 100 Wh | 360 kJ |
| 250 Wh | 900 kJ |
| 500 Wh | 1,800 kJ |
| 1,000 Wh | 3,600 kJ |
Common questions
Is Wh to kJ 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 Kilojoules to Watt-hours converter.
Mistakes to avoid
Dropping the units
A bare number without a unit is easy to misread later. Always write the unit with the result.
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.
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
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.
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.
Many conversion factors are exact by definition. The inch has been defined as exactly 2.54 centimetres since 1959, and the pound as exactly 0.45359237 kilograms, so conversions involving them can be as precise as you need.
For any value, use the Watt-hours to Kilojoules Converter or browse all energy converters.
Run your own numbers: Watt-hours to Kilojoules Converter