Attojoule is 1e-18 joule units.
Attojoules to Kilocalories Converter — aJ to kcal
Convert Attojoule (aJ) to Kilocalorie (kcal) using the exact conversion factor (1 attojoule = 2.390057e-22 kilocalorie). See the formula, worked examples, and conversion table.
Attojoules to Kilocalories 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.
A kilocalorie is 1,000 calories.
Result = input x 1e-18 / 4184.
Energy units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Attojoules to Kilocalories
Attojoule and Kilocalorie 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. Specifically: Attojoule is 1e-18 joule units, and a kilocalorie is 1,000 calories.
Formula
kilocalories = attojoules × 2.390057e-22
This factor comes from each unit's defined relationship to the category's base unit: 1 attojoule equals 1e-18 base units, and 1 kilocalorie equals 4184 base units, so dividing one by the other gives the direct attojoule-to-kilocalorie factor of 2.390057e-22.
Simple example
1 aJ × 2.390057e-22 = 2.390057e-22 kcal
1 attojoule = 2.390057e-22 kilocalories.
Real-world example
100 aJ × 2.390057e-22 = 2.390057e-20 kcal
100 attojoules = 2.390057e-20 kilocalories.
Conversion table
| Attojoule (aJ) | Kilocalorie (kcal) |
|---|---|
| 1 aJ | 2.390057e-22 kcal |
| 10 aJ | 2.390057e-21 kcal |
| 50 aJ | 1.195029e-20 kcal |
| 100 aJ | 2.390057e-20 kcal |
| 500 aJ | 1.195029e-19 kcal |
| 1,000 aJ | 2.390057e-19 kcal |
Reverse conversion: Kilocalorie to Attojoule
2.390057e-22 kcal × 4.184e+21 = 0.9999998488 aJ
2.390057e-22 kilocalories = 0.9999998488 attojoules.
attojoules = kilocalories × 4.184e+21
For a page dedicated to this direction, see Kilocalorie to Attojoule.
Understanding the Attojoule (aJ)
Attojoule is 1e-18 joule units.
Understanding the Kilocalorie (kcal)
A kilocalorie is 1,000 calories.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many kilocalories are in 1 attojoule?
1 attojoule equals 2.390057e-22 kilocalories, using the exact defined conversion factor rather than an estimate.
How do I convert attojoule to kilocalorie?
Multiply the attojoule value by 2.390057e-22. The converter above does this instantly to whatever precision you set.
How do I convert kilocalorie back to attojoule?
Use the reverse factor: 1 kilocalorie equals 4.184e+21 attojoules. You can also use the swap control in the converter above to flip the direction instantly.
What is a attojoule?
Attojoule (aJ) is a unit of engineering.
What is a kilocalorie?
Kilocalorie (kcal) is a unit of engineering.
Is the attojoule to kilocalorie conversion exact?
Yes. Both attojoule and kilocalorie are defined by fixed standards rather than physical artifacts, so the factor of 2.390057e-22 used above is exact to as many digits as you choose to display.
Why do engineering unit conventions vary so much by region and industry?
Pressure, force, and stress can be expressed in metric (pascal, newton), US customary (psi, pound-force), or older and industry-specific units (atmosphere, torr, kip) depending on the country, industry, and even the equipment manufacturer, which is why engineers routinely need to convert between them when working across specs from different sources.