A thermochemical calorie is 4.184 joules.
Calories to Hectojoules Converter — cal to hJ
Convert Calorie (cal) to Hectojoule (hJ) using the exact conversion factor (1 calorie = 0.04184 hectojoule). See the formula, worked examples, conversion table, history, and common uses.
Calories to Hectojoules 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.
Hectojoule is 100 joule units.
Result = input x 4.184 / 100.
Energy uses the joule as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Calories to Hectojoules
Calorie and Hectojoule 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
hectojoules = calories × 0.04184
This factor comes from each unit's defined relationship to the category's base unit: 1 calorie equals 4.184 base units, and 1 hectojoule equals 100 base units, so dividing one by the other gives the direct calorie-to-hectojoule factor of 0.04184.
Simple example
1 cal × 0.04184 = 0.04184 hJ
1 calorie = 0.04184 hectojoules.
Real-world example
100 cal × 0.04184 = 4.184 hJ
100 calories = 4.184 hectojoules.
Conversion table
| Calorie (cal) | Hectojoule (hJ) |
|---|---|
| 1 cal | 0.04184 hJ |
| 10 cal | 0.4184 hJ |
| 100 cal | 4.184 hJ |
| 500 cal | 20.92 hJ |
| 1,000 cal | 41.84 hJ |
| 2,000 cal | 83.68 hJ |
Reverse conversion: Hectojoule to Calorie
0.04184 hJ × 23.90057361 = 1 cal
0.04184 hectojoules = 1 calorie.
calories = hectojoules × 23.9005736138
For a page dedicated to this direction, see Hectojoule 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 Hectojoule (hJ)
Hectojoule is 100 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 hectojoules are in 1 calorie?
1 calorie equals 0.04184 hectojoules, using the exact defined conversion factor rather than an estimate.
How do I convert calorie to hectojoule?
Multiply the calorie value by 0.04184. The converter above does this instantly to whatever precision you set.
How do I convert hectojoule back to calorie?
Use the reverse factor: 1 hectojoule equals 23.90057361 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 hectojoule?
Hectojoule (hJ) is a unit of energy.
Is the calorie to hectojoule 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')