A kilocalorie is 1,000 calories.
Kilocalories to Femtojoules Converter — kcal to fJ
Convert Kilocalorie (kcal) to Femtojoule (fJ) using the exact conversion factor (1 kilocalorie = 4.184e+18 femtojoule). See the formula, worked examples, and conversion table.
Kilocalories to Femtojoules converter
Converter
Energy Converter
Convert joules, calories, kilowatt-hours, BTU, electronvolts, therms, and mechanical work units.
Context values
Some unit families need one extra value for a physically accurate result.
Femtojoule is 1e-15 joule units.
Result = input x 4184 / 1e-15.
Energy uses the joule as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Kilocalories to Femtojoules
Kilocalorie and Femtojoule both measure energy, and the conversion is especially useful for comparing nutrition labels (kilocalories) against scientific energy figures (joules). Specifically: A kilocalorie is 1,000 calories, and femtojoule is 1e-15 joule units.
Formula
femtojoules = kilocalories × 4.184e+18
This factor comes from each unit's defined relationship to the category's base unit: 1 kilocalorie equals 4184 base units, and 1 femtojoule equals 1e-15 base units, so dividing one by the other gives the direct kilocalorie-to-femtojoule factor of 4.184e+18.
Simple example
1 kcal × 4.184e+18 = 4.184e+18 fJ
1 kilocalorie = 4.184e+18 femtojoules.
Real-world example
100 kcal × 4.184e+18 = 4.184e+20 fJ
100 kilocalories = 4.184e+20 femtojoules.
Conversion table
| Kilocalorie (kcal) | Femtojoule (fJ) |
|---|---|
| 1 kcal | 4.184e+18 fJ |
| 10 kcal | 4.184e+19 fJ |
| 100 kcal | 4.184e+20 fJ |
| 500 kcal | 2.092e+21 fJ |
| 1,000 kcal | 4.184e+21 fJ |
| 2,000 kcal | 8.368e+21 fJ |
Reverse conversion: Femtojoule to Kilocalorie
4.184e+18 fJ × 2.390057e-19 = 1 kcal
4.184e+18 femtojoules = 1 kilocalorie.
kilocalories = femtojoules × 2.390057e-19
For a page dedicated to this direction, see Femtojoule to Kilocalorie.
Understanding the Kilocalorie (kcal)
A kilocalorie is 1,000 calories.
Understanding the Femtojoule (fJ)
Femtojoule is 1e-15 joule units.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many femtojoules are in 1 kilocalorie?
1 kilocalorie equals 4.184e+18 femtojoules, using the exact defined conversion factor rather than an estimate.
How do I convert kilocalorie to femtojoule?
Multiply the kilocalorie value by 4.184e+18. The converter above does this instantly to whatever precision you set.
How do I convert femtojoule back to kilocalorie?
Use the reverse factor: 1 femtojoule equals 2.390057e-19 kilocalories. You can also use the swap control in the converter above to flip the direction instantly.
What is a kilocalorie?
Kilocalorie (kcal) is a unit of energy.
What is a femtojoule?
Femtojoule (fJ) is a unit of energy.
Is the kilocalorie to femtojoule conversion exact?
Yes. Both kilocalorie and femtojoule are defined by fixed standards rather than physical artifacts, so the factor of 4.184e+18 used above is exact to as many digits as you choose to display.