# Horsepower-hour

Horsepower-hour
Unit of Energy
Symbol hp·h
Unit conversions
1 hp·h in ... ... is equal to ...
SI units    2.685 MJ
CGS units    2.685×1013 erg
English Engineering Units    1.98×106 ft⋅lbf

A horsepower-hour (hph or hp·h) is an outdated unit of energy, not used in the SI system of units. The unit represents an amount of work a horse is supposed capable of delivering during an hour (1 (one) horsepower integrated over a time interval of an hour). Based on differences in the definition of what constitutes the 'power of a horse', a horsepower-hour differs slightly from the German "Pferdestärkenstunde" (PSh):

1.014 PSh = 1 hph = 1,980,000 lbf·ft = 0.7457 kWh.
1 PSh = 0.73549875 kW·h = 2647.7955 kJ (exactly by definition)

The horsepower-hour is still used in the railroad industry when sharing motive power (locomotives.) For example, if Railroad A borrows a 2,500 horsepower locomotive from Railroad B and operates it for twelve hours, Railroad A owes a debt of (2,500 hp × 12 h) = 30,000 hp·h. Railroad A may repay the debt by loaning Railroad B a 3,000 horsepower locomotive for ten hours.[1]

## References

1. ^ "Archived copy". Archived from the original on 2008-12-04. Retrieved 2009-05-25.