Convert Horsepower-Hours to Attojoules
Convert Horsepower-Hours (hp·h) to Attojoules (aJ) instantly and accurately.
Conversion Formula
aJ = hp·h × 2.684519538e+24
About Horsepower-Hours
A horsepower-hour (hp·h) is the energy from one mechanical horsepower (745.6999 W) for one hour - exactly 2,684,519.54 J ≈ 2.685 MJ. James Watt coined the horsepower to compare his steam engines with mine horses; billing in hp·h preceded the kilowatt-hour tariff. The metric horsepower (PS = 75 kgf·m/s = 735.499 W) gives a slightly smaller metric-hp·h = 2,647,795 J, used in European and Japanese engine datasheets. Today the hp·h appears in marine engineering logs, mining energy accounting, and vintage industrial equipment. 1 hp·h = 2.6845 MJ = 0.74570 kWh = 641.19 kcal.
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.
Quick Reference Table
| Horsepower-Hours (hp·h) | Attojoules (aJ) |
|---|---|
| 1 hp·h | 2.685 × 1024 aJ |
| 2 hp·h | 5.369 × 1024 aJ |
| 5 hp·h | 1.342 × 1025 aJ |
| 10 hp·h | 2.685 × 1025 aJ |
| 25 hp·h | 6.711 × 1025 aJ |
| 50 hp·h | 1.342 × 1026 aJ |
| 100 hp·h | 2.685 × 1026 aJ |