A thermochemical calorie is 4.184 joules.
Calories to Microjoules Converter — cal to uJ
Convert Calorie (cal) to Microjoule (uJ) using the exact conversion factor (1 calorie = 4,184,000 microjoule). See the formula, worked examples, conversion table, history, and common uses.
Calories to Microjoules converter
Converter
Energy Converter
Convert joules, calories, kilowatt-hours, BTU, electronvolts, therms, and mechanical work units.
Context values
Some unit families need one extra value for a physically accurate result.
Microjoule is 0.000001 joule units.
Result = input x 4.184 / 1e-6.
Energy uses the joule as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Calories to Microjoules
Calorie and Microjoule both measure energy, and the conversion is especially useful for comparing nutrition labels (kilocalories) against scientific energy figures (joules). Calorie is most often used for food energy labeling (as kilocalories, often written 'calories').
Formula
microjoules = calories × 4184000
This factor comes from each unit's defined relationship to the category's base unit: 1 calorie equals 4.184 base units, and 1 microjoule equals 0.000001 base units, so dividing one by the other gives the direct calorie-to-microjoule factor of 4184000.
Simple example
1 cal × 4184000 = 4,184,000 uJ
1 calorie = 4,184,000 microjoules.
Real-world example
100 cal × 4184000 = 418,400,000 uJ
100 calories = 418,400,000 microjoules.
Conversion table
| Calorie (cal) | Microjoule (uJ) |
|---|---|
| 1 cal | 4,184,000 uJ |
| 10 cal | 41,840,000 uJ |
| 100 cal | 418,400,000 uJ |
| 500 cal | 2,092,000,000 uJ |
| 1,000 cal | 4,184,000,000 uJ |
| 2,000 cal | 8,368,000,000 uJ |
Reverse conversion: Microjoule to Calorie
1 uJ × 2.390057e-7 = 2.390057e-7 cal
1 microjoule = 2.390057e-7 calories.
calories = microjoules × 2.390057e-7
For a page dedicated to this direction, see Microjoule 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 Microjoule (uJ)
Microjoule is 0.000001 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 microjoules are in 1 calorie?
1 calorie equals 4,184,000 microjoules, using the exact defined conversion factor rather than an estimate.
How do I convert calorie to microjoule?
Multiply the calorie value by 4184000. The converter above does this instantly to whatever precision you set.
How do I convert microjoule back to calorie?
Use the reverse factor: 1 microjoule equals 2.390057e-7 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 microjoule?
Microjoule (uJ) is a unit of energy.
Is the calorie to microjoule 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')