Convert Femtojoules to Kilocalories
Convert Femtojoules (fJ) to Kilocalories (kcal) instantly and accurately.
Conversion Formula
kcal = fJ × 2.390057361e-19
About Femtojoules
A femtojoule (fJ) is 10⁻¹⁵ J - the scale of gamma-ray photons, molecular motor work, and state-of-the-art digital logic. The electron rest-mass energy is 81.87 fJ; a 100 keV X-ray photon carries 16.02 fJ. A single myosin II motor protein power stroke dissipates ~5-40 fJ. ATP hydrolysis under cellular conditions yields ~80-100 fJ of free energy. Advanced 3 nm CMOS gates switch at ~0.1-1 fJ per operation. Ultrafast fiber laser oscillators produce pulses of 0.1-10 fJ before amplification. 1 fJ = 10⁻¹⁵ J = 6.242 keV.
About Kilocalories
A kilocalorie (kcal) - the food Calorie (capital C) on US and Canadian nutrition labels - is exactly 4,184 J. WHO recommends ~2,000-2,500 kcal/day for adults. Energy density of nutrients: fat 9 kcal/g, carbohydrate 4 kcal/g, protein 4 kcal/g, ethanol 7 kcal/g. Running at 10 km/h burns ~600-800 kcal/h. Standard free energy of ATP hydrolysis is approximately −7.3 kcal/mol (−30.5 kJ/mol). Pre-SI thermodynamic tables in the US and Japan use kcal/mol for reaction enthalpies. 1 kcal = 4,184 J = 4.184 kJ = 3.968 BTU = 1.163 Wh.
Quick Reference Table
| Femtojoules (fJ) | Kilocalories (kcal) |
|---|---|
| 1 fJ | 2.39 × 10-19 kcal |
| 2 fJ | 4.78 × 10-19 kcal |
| 5 fJ | 1.195 × 10-18 kcal |
| 10 fJ | 2.39 × 10-18 kcal |
| 25 fJ | 5.975 × 10-18 kcal |
| 50 fJ | 1.195 × 10-17 kcal |
| 100 fJ | 2.39 × 10-17 kcal |