A kilocalorie (kcal) equals 1,000 small calories and is the unit behind the food "Calorie" shown on nutrition labels.
Kilocalories to Attojoules
Convert Kilocalorie (kcal) to Attojoule (aJ) instantly with an exact formula, conversion table, and FAQ.
Reserved for a responsive leaderboard above the conversion details.
Professional calculator style
World-scale conversion engine
30+ categories
6,500+ units
Instant results
Offline ready
Energy calculator
Energy Converter
Convert kilocalories (kcal) to attojoules (aJ) instantly with formula, conversion table, and FAQ.
Context values
Some unit families need one extra value for a physically accurate result.
A attojoule (aJ) is a metric-prefixed unit of energy equal to 10-18 joules, a fraction of a single joule, using the SI atto prefix.
aJ = kcal × 4.184000000e+21
Results update instantly for Kilocalories to Attojoules conversions.
Reserved above the conversion cards and below the converter.
Formula
aJ = kcal × 4.184000000e+21
kcal = aJ × 2.390057361e-22
Conversion table
| 1 kcal | 4.184000e+21 aJ |
| 5 kcal | 2.092000e+22 aJ |
| 10 kcal | 4.184000e+22 aJ |
| 20 kcal | 8.368000e+22 aJ |
| 50 kcal | 2.092000e+23 aJ |
| 100 kcal | 4.184000e+23 aJ |
| 500 kcal | 2.092000e+24 aJ |
| 1000 kcal | 4.184000e+24 aJ |
Related conversions
Reserved between the cards and the FAQ so the page stays balanced.
How the formula works
Both kilocalorie and attojoule measure the same physical quantity, so converting between them is a single multiplication. Multiply a value in kilocalories by 4.184000000e+21 to get attojoules. To reverse the conversion, multiply a attojoule value by 2.390057361e-22 to get back to kilocalories.
Frequently asked questions
What is Kilocalorie (kcal)?
A kilocalorie (kcal) equals 1,000 small calories and is the unit behind the food "Calorie" shown on nutrition labels.
What is Attojoule (aJ)?
A attojoule (aJ) is a metric-prefixed unit of energy equal to 10-18 joules, a fraction of a single joule, using the SI atto prefix.
How do I convert kilocalories to attojoules?
Multiply the kilocalorie value by 4.184000000e+21 to get the equivalent in attojoules. For example, 5 kcal × 4.184000000e+21 = 2.092000e+22 aJ.
Is this conversion exact?
Yes. Both units are defined against the SI base unit for this dimension, so the factor 4.184000000e+21 is an exact, non-rounded value.
Can I convert attojoules back to kilocalories?
Yes. Divide the attojoule value by 4.184000000e+21, or multiply it by 2.390057361e-22, to get kilocalories.
Reserved between the FAQ and the article so the page stays balanced.
About converting kilocalories to attojoules
A kilocalorie (kcal) equals 1,000 small calories and is the unit behind the food "Calorie" shown on nutrition labels. A attojoule (aJ) is a metric-prefixed unit of energy equal to 10-18 joules, a fraction of a single joule, using the SI atto prefix.
Use this calculator to move between kilocalories and attojoules accurately for homework, engineering, billing, or everyday energy calculations. The Universal Converter uses exact unit factors, so results stay consistent across the site.