Calories to Megajoules
Convert calories to megajoules instantly — one calorie is 4.184e-06 megajoules.
| Calories | Megajoules |
|---|---|
| 1 cal | 4.184e-06 MJ |
| 2 cal | 8.368e-06 MJ |
| 3 cal | 1.2552e-05 MJ |
| 5 cal | 2.092e-05 MJ |
| 10 cal | 4.184e-05 MJ |
| 25 cal | 0.000105 MJ |
| 50 cal | 0.000209 MJ |
| 100 cal | 0.000418 MJ |
How to use
- Enter a value in the Calories field.
- The Megajoules figure appears immediately — no button to press.
- Typing in the Megajoules field converts back to Calories the same way.
- Use the reference table for the values that come up most often.
Calories to Megajoules formula
The factor from calories to megajoules is 4.184e-06.
MJ = cal × 4.184e-06
Why this factor: the calorie and the megajoule are both defined against the joule, so dividing one definition by the other gives 4.184e-06 directly. Both definitions are set out in full below.
To go the other way, divide by 4.184e-06 — or use the Megajoules to Calories converter, which is the same calculation reversed.
Worked example
Take 500 cal and multiply by the factor 4.184e-06: the result is 0.002092 MJ.
500 cal × 4.184e-06 = 0.002092 MJ
The converter above does this for any value you type, in either direction.
What is a calorie?
A calorie is the energy needed to warm one gram of water by one degree Celsius.
Definition: The thermochemical calorie is defined as exactly 4.184 joules.
Where it is used: Chemistry and physics literature, and older engineering references.
Worth knowing: The 'calories' on a nutrition label are actually kilocalories — 1,000 of these. A 500-Calorie meal is 500 kcal, or about 2.1 million joules.
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.
Calories vs Megajoules
The calorie is a specialized 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 calorie?
One calorie equals 4.184e-06 megajoules.
What is the formula to convert calories to megajoules?
Multiply the number of calories by 4.184e-06. To reverse it, divide by 4.184e-06 instead.
How do I convert megajoules back to calories?
Divide by 4.184e-06, which is the same as multiplying by 239005.736.
How many megajoules are in 10 calories?
10 cal works out to 4.184e-05 MJ.
Is there anything to watch out for with calories?
The 'calories' on a nutrition label are actually kilocalories — 1,000 of these. A 500-Calorie meal is 500 kcal, or about 2.1 million joules.
How is the calorie defined?
The thermochemical calorie is defined as exactly 4.184 joules.