A horsepower-hour (symbol: hp⋅h) is an outdated unit of

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...

, not used in the International System of Units. The unit represents an amount of

work Work may refer to: * Work (human activity), intentional activity people perform to support themselves, others, or the community ** Manual labour, physical work done by humans ** House work, housework, or homemaking ** Working animal, an animal t ...

a horse is supposed capable of delivering during an hour (1

horsepower Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are t ...

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 hp⋅h = 1,980,000 lbf⋅ft = 0.7457 kW⋅h. :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.

References

Imperial units Units of energy {{measurement-stub