How to Convert Megajoules to Watt-hours (MJ 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 megajoules into watt-hours by hand, with examples and a quick-reference table.
The conversion
To convert megajoules to watt-hours, multiply the value by 277.7777777778. To go the other way, divide by the same number (or multiply by 0.0036). For a quick estimate, multiply by about 280.
Watt-hours = megajoules × 277.7777777778
Worked examples
- 3 MJ = 833.3333 Wh
- 12.5 MJ = 3,472.22 Wh
- 75 MJ = 20,833.33 Wh
Megajoules to Watt-hours table
| Megajoules | Watt-hours |
|---|---|
| 1 MJ | 277.7778 Wh |
| 2 MJ | 555.5556 Wh |
| 5 MJ | 1,388.89 Wh |
| 10 MJ | 2,777.78 Wh |
| 20 MJ | 5,555.56 Wh |
| 25 MJ | 6,944.44 Wh |
| 50 MJ | 13,888.89 Wh |
| 100 MJ | 27,777.78 Wh |
| 250 MJ | 69,444.44 Wh |
| 500 MJ | 138,888.89 Wh |
| 1,000 MJ | 277,777.78 Wh |
Common questions
Is MJ 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 Megajoules converter.
Mistakes to avoid
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.
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
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.
A conversion table is handy for common values, but a calculator is faster and avoids interpolation errors for anything in between.
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 Megajoules to Watt-hours Converter or browse all energy converters.
Run your own numbers: Megajoules to Watt-hours Converter