Convert Attojoules to Calories
Convert Attojoules (aJ) to Calories (cal) instantly and accurately.
Conversion Formula
cal = aJ × 2.390057361e-19
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 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
| Attojoules (aJ) | Calories (cal) |
|---|---|
| 1 aJ | 2.39 × 10-19 cal |
| 2 aJ | 4.78 × 10-19 cal |
| 5 aJ | 1.195 × 10-18 cal |
| 10 aJ | 2.39 × 10-18 cal |
| 25 aJ | 5.975 × 10-18 cal |
| 50 aJ | 1.195 × 10-17 cal |
| 100 aJ | 2.39 × 10-17 cal |