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.
Attojoules to Kilocalories
Convert Attojoule (aJ) to Kilocalorie (kcal) instantly with an exact formula, conversion table, and FAQ.
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Convert attojoules (aJ) to kilocalories (kcal) instantly with formula, conversion table, and FAQ.
Context values
Some unit families need one extra value for a physically accurate result.
A kilocalorie (kcal) equals 1,000 small calories and is the unit behind the food "Calorie" shown on nutrition labels.
kcal = aJ × 2.390057361e-22
Results update instantly for Attojoules to Kilocalories conversions.
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Formula
kcal = aJ × 2.390057361e-22
aJ = kcal × 4.184000000e+21
Conversion table
| 1 aJ | 2.390057e-22 kcal |
| 5 aJ | 1.195029e-21 kcal |
| 10 aJ | 2.390057e-21 kcal |
| 20 aJ | 4.780115e-21 kcal |
| 50 aJ | 1.195029e-20 kcal |
| 100 aJ | 2.390057e-20 kcal |
| 500 aJ | 1.195029e-19 kcal |
| 1000 aJ | 2.390057e-19 kcal |
Related conversions
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How the formula works
Both attojoule and kilocalorie measure the same physical quantity, so converting between them is a single multiplication. Multiply a value in attojoules by 2.390057361e-22 to get kilocalories. To reverse the conversion, multiply a kilocalorie value by 4.184000000e+21 to get back to attojoules.
Frequently asked questions
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.
What is Kilocalorie (kcal)?
A kilocalorie (kcal) equals 1,000 small calories and is the unit behind the food "Calorie" shown on nutrition labels.
How do I convert attojoules to kilocalories?
Multiply the attojoule value by 2.390057361e-22 to get the equivalent in kilocalories. For example, 5 aJ × 2.390057361e-22 = 1.195029e-21 kcal.
Is this conversion exact?
Yes. Both units are defined against the SI base unit for this dimension, so the factor 2.390057361e-22 is an exact, non-rounded value.
Can I convert kilocalories back to attojoules?
Yes. Divide the kilocalorie value by 2.390057361e-22, or multiply it by 4.184000000e+21, to get attojoules.
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About converting attojoules to kilocalories
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. A kilocalorie (kcal) equals 1,000 small calories and is the unit behind the food "Calorie" shown on nutrition labels.
Use this calculator to move between attojoules and kilocalories accurately for homework, engineering, billing, or everyday energy calculations. The Universal Converter uses exact unit factors, so results stay consistent across the site.