A (small) calorie is a thermochemical unit of heat energy equal to 4.184 joules, historically the energy needed to raise 1 gram of water by 1°C.
Calories to Attojoules
Convert Calorie (cal) to Attojoule (aJ) instantly with an exact formula, conversion table, and FAQ.
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Convert calories (cal) 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 = cal × 4.184000000e+18
Results update instantly for Calories to Attojoules conversions.
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Formula
aJ = cal × 4.184000000e+18
cal = aJ × 2.390057361e-19
Conversion table
| 1 cal | 4.184000e+18 aJ |
| 5 cal | 2.092000e+19 aJ |
| 10 cal | 4.184000e+19 aJ |
| 20 cal | 8.368000e+19 aJ |
| 50 cal | 2.092000e+20 aJ |
| 100 cal | 4.184000e+20 aJ |
| 500 cal | 2.092000e+21 aJ |
| 1000 cal | 4.184000e+21 aJ |
Related conversions
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How the formula works
Both calorie and attojoule measure the same physical quantity, so converting between them is a single multiplication. Multiply a value in calories by 4.184000000e+18 to get attojoules. To reverse the conversion, multiply a attojoule value by 2.390057361e-19 to get back to calories.
Frequently asked questions
What is Calorie (cal)?
A (small) calorie is a thermochemical unit of heat energy equal to 4.184 joules, historically the energy needed to raise 1 gram of water by 1°C.
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 calories to attojoules?
Multiply the calorie value by 4.184000000e+18 to get the equivalent in attojoules. For example, 5 cal × 4.184000000e+18 = 2.092000e+19 aJ.
Is this conversion exact?
Yes. Both units are defined against the SI base unit for this dimension, so the factor 4.184000000e+18 is an exact, non-rounded value.
Can I convert attojoules back to calories?
Yes. Divide the attojoule value by 4.184000000e+18, or multiply it by 2.390057361e-19, to get calories.
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About converting calories to attojoules
A (small) calorie is a thermochemical unit of heat energy equal to 4.184 joules, historically the energy needed to raise 1 gram of water by 1°C. 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 calories 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.