A thermochemical calorie is 4.184 joules.
Calories to Megajoules Converter — cal to MJ
Convert Calorie (cal) to Megajoule (MJ) using the exact conversion factor (1 calorie = 0.000004184 megajoule). See the formula, worked examples, conversion table, history, and common uses.
Calories to Megajoules converter
Converter
Engineering Converter
Convert common stress, force, torque, power, and energy units used in engineering.
Context values
Some unit families need one extra value for a physically accurate result.
Megajoule is 1000000 joule units.
Result = input x 4.184 / 1e+6.
Energy units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Calories to Megajoules
Calorie and Megajoule both measure a quantity used in structural or mechanical engineering — commonly stress, pressure, force, torque, power, or energy — where converting between the unit conventions used in different regions, industries, or equipment specifications is a routine part of design work. Calorie is most often used for food energy labeling (as kilocalories, often written 'calories').
Formula
megajoules = calories × 0.000004184
This factor comes from each unit's defined relationship to the category's base unit: 1 calorie equals 4.184 base units, and 1 megajoule equals 1000000 base units, so dividing one by the other gives the direct calorie-to-megajoule factor of 0.000004184.
Simple example
1 cal × 0.000004184 = 0.000004184 MJ
1 calorie = 0.000004184 megajoules.
Real-world example
100 cal × 0.000004184 = 0.0004184 MJ
100 calories = 0.0004184 megajoules.
Conversion table
| Calorie (cal) | Megajoule (MJ) |
|---|---|
| 1 cal | 0.000004184 MJ |
| 10 cal | 0.00004184 MJ |
| 50 cal | 0.0002092 MJ |
| 100 cal | 0.0004184 MJ |
| 500 cal | 0.002092 MJ |
| 1,000 cal | 0.004184 MJ |
Reverse conversion: Megajoule to Calorie
0.000004184 MJ × 239005.7361 = 1 cal
0.000004184 megajoules = 1 calorie.
calories = megajoules × 239005.736138
For a page dedicated to this direction, see Megajoule to Calorie.
Understanding the Calorie
Calorie (cal) measures energy. The thermochemical calorie used in this converter is defined as exactly 4.184 joules. It is classified as a Non-SI unit (limited use with SI).
Where it's used: Nutrition labeling in the US and several other countries still commonly uses the kilocalorie (as 'Calorie')
Calorie vs. Calorie (kilocalorie). Food labels' capitalized 'Calorie' is actually one kilocalorie (1,000 small calories) — a long-standing labeling convention that causes frequent confusion.
Uses of the Calorie today
- Food energy labeling (as kilocalories, often written 'Calories')
- Historical chemistry and thermodynamics contexts
History of the Calorie
The calorie was originally defined in the early 19th century as the heat needed to raise one gram of water by one degree Celsius, but different scientific traditions defined it at slightly different reference temperatures, producing several close but non-identical 'calorie' values historically (15 °C calorie, mean calorie, thermochemical calorie).
To resolve this ambiguity, the thermochemical calorie was fixed by convention at exactly 4.184 joules; the very similar International Table calorie is fixed at exactly 4.1868 joules. The nutritional 'Calorie' seen on food labels is actually a kilocalorie (1,000 calories).
Historical origin. Calorie was not the invention of a single named person; it developed through the process described above.
Understanding the Megajoule (MJ)
Megajoule is 1000000 joule units.
Calorie — sources
- NIST Special Publication 811 — Documents the thermochemical calorie's exact joule equivalence.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many megajoules are in 1 calorie?
1 calorie equals 0.000004184 megajoules, using the exact defined conversion factor rather than an estimate.
How do I convert calorie to megajoule?
Multiply the calorie value by 0.000004184. The converter above does this instantly to whatever precision you set.
How do I convert megajoule back to calorie?
Use the reverse factor: 1 megajoule equals 239,005.7361 calories. You can also use the swap control in the converter above to flip the direction instantly.
What is a calorie?
Calorie (cal) measures energy. The thermochemical calorie used in this converter is defined as exactly 4.184 joules. It is classified as a Non-SI unit (limited use with SI).
What is a megajoule?
Megajoule (MJ) is a unit of engineering.
Is the calorie to megajoule conversion exact?
Yes. The thermochemical calorie used in this converter is defined as exactly 4.184 joules. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
What is the difference between calorie vs. calorie (kilocalorie)?
Food labels' capitalized 'Calorie' is actually one kilocalorie (1,000 small calories) — a long-standing labeling convention that causes frequent confusion.
Where is the calorie still used today?
Nutrition labeling in the US and several other countries still commonly uses the kilocalorie (as 'Calorie')