How to Convert Watt-hours to Megajoules (Wh to MJ)
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 megajoules by hand, with examples and a quick-reference table.
The conversion
To convert watt-hours to megajoules, multiply the value by 0.0036. To go the other way, divide by the same number (or multiply by 277.7777777778). For a quick estimate, multiply by about 0.0036.
Megajoules = watt-hours × 0.0036
Worked examples
- 3 Wh = 0.0108 MJ
- 12.5 Wh = 0.045 MJ
- 75 Wh = 0.27 MJ
Watt-hours to Megajoules table
| Watt-hours | Megajoules |
|---|---|
| 1 Wh | 0.0036 MJ |
| 2 Wh | 0.0072 MJ |
| 5 Wh | 0.018 MJ |
| 10 Wh | 0.036 MJ |
| 20 Wh | 0.072 MJ |
| 25 Wh | 0.09 MJ |
| 50 Wh | 0.18 MJ |
| 100 Wh | 0.36 MJ |
| 250 Wh | 0.9 MJ |
| 500 Wh | 1.8 MJ |
| 1,000 Wh | 3.6 MJ |
Common questions
Is Wh to MJ 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 Megajoules to Watt-hours converter.
Mistakes to avoid
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.
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
A conversion table is handy for common values, but a calculator is faster and avoids interpolation errors for anything in between.
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.
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.
For any value, use the Watt-hours to Megajoules Converter or browse all energy converters.
Run your own numbers: Watt-hours to Megajoules Converter