Joules to Megajoules
Type a value in either box to convert between joules and megajoules. The factor is 1e-06.
| Joules | Megajoules |
|---|---|
| 1 J | 1e-06 MJ |
| 2 J | 2e-06 MJ |
| 3 J | 3e-06 MJ |
| 5 J | 5e-06 MJ |
| 10 J | 1e-05 MJ |
| 25 J | 2.5e-05 MJ |
| 50 J | 5e-05 MJ |
| 100 J | 0.0001 MJ |
How to use
- Enter a value in the Joules field.
- The Megajoules figure appears immediately — no button to press.
- Typing in the Megajoules field converts back to Joules the same way.
- Use the reference table for the values that come up most often.
Joules to Megajoules formula
To convert joules to megajoules, multiply by 1e-06.
MJ = J × 1e-06
Why this factor: the joule and the megajoule are both defined against the joule, so dividing one definition by the other gives 1e-06 directly. Both definitions are set out in full below.
To go the other way, divide by 1e-06 — or use the Megajoules to Joules converter, which is the same calculation reversed.
Worked example
Given 100 J, multiplying by 1e-06 yields 0.0001 MJ.
100 J × 1e-06 = 0.0001 MJ
The converter above does this for any value you type, in either direction.
What is a joule?
The joule is the SI unit of energy — the work done by one newton acting over one meter.
Definition: Defined as 1 N·m, equivalently one watt-second. Named after James Prescott Joule.
Where it is used: All scientific energy calculations, food energy on European labels, and mechanical work.
What is a megajoule?
A megajoule is one million joules, used for substantial energy quantities.
Definition: Exactly 1×10⁶ joules. One kilowatt-hour is exactly 3.6 MJ.
Where it is used: Fuel energy content, natural gas billing, and industrial energy accounting.
Joules vs Megajoules
The joule is an SI unit while the megajoule is a metric unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many megajoules are in a joule?
One joule equals 1e-06 megajoules.
What is the formula to convert joules to megajoules?
Multiply the number of joules by 1e-06. To reverse it, divide by 1e-06 instead.
How do I convert megajoules back to joules?
Divide by 1e-06, which is the same as multiplying by 1000000.
How many megajoules are in 10 joules?
10 J works out to 1e-05 MJ.
How is the joule defined?
Defined as 1 N·m, equivalently one watt-second. Named after James Prescott Joule.