A kilocalorie (kcal) equals 1,000 small calories and is the unit behind the food "Calorie" shown on nutrition labels.
Kilocalories to Femtojoules
Convert Kilocalorie (kcal) to Femtojoule (fJ) instantly with an exact formula, conversion table, and FAQ.
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Convert kilocalories (kcal) to femtojoules (fJ) instantly with formula, conversion table, and FAQ.
Context values
Some unit families need one extra value for a physically accurate result.
A femtojoule (fJ) is a metric-prefixed unit of energy equal to 10-15 joules, a fraction of a single joule, using the SI femto prefix.
fJ = kcal × 4.184000000e+18
Results update instantly for Kilocalories to Femtojoules conversions.
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Formula
fJ = kcal × 4.184000000e+18
kcal = fJ × 2.390057361e-19
Conversion table
| 1 kcal | 4.184000e+18 fJ |
| 5 kcal | 2.092000e+19 fJ |
| 10 kcal | 4.184000e+19 fJ |
| 20 kcal | 8.368000e+19 fJ |
| 50 kcal | 2.092000e+20 fJ |
| 100 kcal | 4.184000e+20 fJ |
| 500 kcal | 2.092000e+21 fJ |
| 1000 kcal | 4.184000e+21 fJ |
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How the formula works
Both kilocalorie and femtojoule measure the same physical quantity, so converting between them is a single multiplication. Multiply a value in kilocalories by 4.184000000e+18 to get femtojoules. To reverse the conversion, multiply a femtojoule value by 2.390057361e-19 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 Femtojoule (fJ)?
A femtojoule (fJ) is a metric-prefixed unit of energy equal to 10-15 joules, a fraction of a single joule, using the SI femto prefix.
How do I convert kilocalories to femtojoules?
Multiply the kilocalorie value by 4.184000000e+18 to get the equivalent in femtojoules. For example, 5 kcal × 4.184000000e+18 = 2.092000e+19 fJ.
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 femtojoules back to kilocalories?
Yes. Divide the femtojoule value by 4.184000000e+18, or multiply it by 2.390057361e-19, to get kilocalories.
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About converting kilocalories to femtojoules
A kilocalorie (kcal) equals 1,000 small calories and is the unit behind the food "Calorie" shown on nutrition labels. A femtojoule (fJ) is a metric-prefixed unit of energy equal to 10-15 joules, a fraction of a single joule, using the SI femto prefix.
Use this calculator to move between kilocalories and femtojoules accurately for homework, engineering, billing, or everyday energy calculations. The Universal Converter uses exact unit factors, so results stay consistent across the site.