Authoritative definitions of the International System of Units and SI prefixes.
Dedicated unit pair
Megajoules to Watt-hours
Convert MJ to Wh instantly, then review the formula, assumptions, and rounding guidance.
Energy, work, heat & powerInstant result
Decimals
Formula result = input × 1000000 ÷ 3600. 1 MJ = 277.7778 Wh
Common examples
One value, several units
Joules1,000,000 J
Kilojoules1,000 kJ
Watt-hours277.7778 Wh
Kilowatt-hours0.2778 kWh
Thermochemical calories239,005.7361 cal
Kilocalories239.0057 kcal
BTU (International Table)947.8171 BTU
Conversion table
| MJ | Wh |
|---|---|
| 1 MJ | 277.7778 Wh |
| 2 MJ | 555.5556 Wh |
| 5 MJ | 1,388.8889 Wh |
| 10 MJ | 2,777.7778 Wh |
| 25 MJ | 6,944.4444 Wh |
| 50 MJ | 13,888.8889 Wh |
| 100 MJ | 27,777.7778 Wh |
Conversion chart
1 MJ277.7778 Wh
5 MJ1,388.8889 Wh
10 MJ2,777.7778 Wh
25 MJ6,944.4444 Wh
50 MJ13,888.8889 Wh
Worked example
1 kilowatt-hour equals exactly 3.6 megajoules.
Unit definition
Megajoules (MJ) One megajoules equals 1,000,000 joule.
Unit history
Megajoules is represented here using its modern SI definition or an internationally accepted relationship to an SI base unit.
Step by step
1. Parse the value, including fractions.
2. Convert MJ to joule.
3. Convert the base value to Wh and apply your display precision.
Understand the result before using it
Megajoules to Watt-hours converts a value measured in Megajoules (MJ) into the equivalent value in Watt-hours (Wh). The numerical value changes because the size and definition of the selected unit changes; the underlying quantity does not.
Calculated result
The conversion follows the displayed unit relationship. Display rounding can hide additional digits, and measured inputs cannot become more accurate merely by changing units.
Formula, assumptions, and example
Formula
result = input × 1000000 ÷ 3600
Assumptions
- Megajoules and Watt-hours represent the same energy, work & heat quantity.
- The input is expressed in MJ; the output is expressed in Wh.
- The unit definitions and conventional relationship shown on this page apply.
Worked example
1 MJ = 277.777777778 Wh. For another value, apply the same relationship and round only to the precision your source measurement supports.
When to use it
Good uses
- Read a MJ measurement in a document that expects Wh.
- Compare a megajoules value with a value reported in watt-hours.
- Check the MJ-to-Wh arithmetic before copying the result into another calculation.
Limitations
Common mistakes to avoid
- Do not confuse MJ with another unit that has a similar name or symbol.
- Round the output to a precision justified by the original measurement.
- Verify safety-critical, regulated, laboratory, and contractual conversions against the controlling standard.
Sources and further reading
These references explain the underlying standards or provide authoritative context. Your own contract, institution, clinician, product documentation, local code, or governing standard may be the controlling source.
Guidance on unit names, symbols, conversions, and numerical presentation.
Questions about this calculation
How do I convert Megajoules to Watt-hours?
result = input × 1000000 ÷ 3600 Using the displayed relationship, 1 MJ equals 277.777777778 Wh.
How many Watt-hours are in one Megajoules?
One Megajoules is 277.777777778 Watt-hours. The displayed digits may be rounded.
Can I reverse the MJ to Wh conversion?
Yes. Swap the source and target units in the converter. The reverse relationship converts Wh back to MJ.
Is the Megajoules to Watt-hours result exact?
The conversion follows the displayed unit relationship. Display rounding can hide additional digits, and measured inputs cannot become more accurate merely by changing units.