Convert Femtojoules to Calories
Convert Femtojoules (fJ) to Calories (cal) instantly and accurately.
Conversion Formula
cal = fJ × 2.390057361e-16
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 Calories
A calorie (cal) - the thermochemical calorie - is exactly 4.184 J, defined as the heat to raise 1 g of water by 1°C. Standard since 1954. The calorie is the fundamental unit of heat measurement in thermochemistry: glucose combustion releases 669.9 kcal/mol; water vaporisation requires 539.7 cal/g. Bond dissociation energies in quantum chemistry are often quoted in kcal/mol. Note: the dietary Calorie (capital C) on food labels is 1 kcal = 4,184 J - a factor-of-1,000 difference that causes persistent confusion. 1 cal = 4.184 J = 1.163 × 10⁻³ Wh.
Quick Reference Table
| Femtojoules (fJ) | Calories (cal) |
|---|---|
| 1 fJ | 2.39 × 10-16 cal |
| 2 fJ | 4.78 × 10-16 cal |
| 5 fJ | 1.195 × 10-15 cal |
| 10 fJ | 2.39 × 10-15 cal |
| 25 fJ | 5.975 × 10-15 cal |
| 50 fJ | 1.195 × 10-14 cal |
| 100 fJ | 2.39 × 10-14 cal |