Convert Attojoules to Kilocalories
Convert Attojoules (aJ) to Kilocalories (kcal) instantly and accurately.
Conversion Formula
kcal = aJ × 2.390057361e-22
About Attojoules
An attojoule (aJ) is 10⁻¹⁸ J - the scale of individual X-ray photons and superconducting qubit circuits. A 1 keV X-ray photon carries 160 aJ; a visible green photon (~550 nm) carries ~0.36 aJ. Josephson junction energies in superconducting qubits are set in tens to hundreds of aJ to achieve quantum coherence at millikelvin temperatures. XRISM's cryogenic TES X-ray spectrometer resolves individual photon energies at the hundreds-of-aJ level with ~7 eV FWHM resolution. 1 aJ = 10⁻¹⁸ J = 6.242 eV.
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
| Attojoules (aJ) | Kilocalories (kcal) |
|---|---|
| 1 aJ | 2.39 × 10-22 kcal |
| 2 aJ | 4.78 × 10-22 kcal |
| 5 aJ | 1.195 × 10-21 kcal |
| 10 aJ | 2.39 × 10-21 kcal |
| 25 aJ | 5.975 × 10-21 kcal |
| 50 aJ | 1.195 × 10-20 kcal |
| 100 aJ | 2.39 × 10-20 kcal |