A horsepower-hour is an outdated unit of energy, not used in the International System of Units. The unit represents an amount of work a horse is supposed capable of delivering during 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