Joules to Horsepower-hours (J to hp⋅h)
1 joule equals 3.72506136×10⁻⁷ horsepower-hours (rounded).
How to convert joules to horsepower-hours
To convert joules to horsepower-hours, multiply the number of joules by 3.72506136×10⁻⁷. The factor is rounded to 10 significant digits. To go the other way, multiply horsepower-hours by 2,684,519.538 (rounded).
horsepower-hours = joules × 3.72506136×10⁻⁷
Example: 10 joules = 0.00000372506136 horsepower-hours.
The 'calorie' on food labels is really a kilocalorie. The thermochemical calorie (4.184 J) is used here unless marked IT.
About these units
Joule (J)
The SI unit of energy: the work done by a force of one newton over one meter, or one watt for one second.
James Prescott Joule was born in Salford on 24 December 1818, the son of a wealthy brewer, and later ran the family brewery while treating science as a serious hobby. In June 1845 he told a British Association meeting in Cambridge about his best-known experiment: a falling weight turned a paddle wheel inside an insulated barrel of water, and the water warmed up. Mechanical work turned into heat at a fixed rate, which supported energy conservation and undermined the caloric theory of heat.
The unit came later. On 23 August 1882 Carl Wilhelm Siemens proposed at a British Association meeting that a unit of heat equal to 10 million ergs be named the joule, and in 1889 the second International Electrical Congress adopted it alongside the watt. Joule died that same year. In 1948 the CGPM added that the joule should be preferred to the calorie as the unit of heat, and it entered the SI in 1960.
For scale, one joule is about the energy needed to lift an apple of roughly 102 g by one meter. A 56 g tennis ball moving at 6 m/s carries about one joule of kinetic energy.
The joule is the reference unit for energy on this site.
Sources: Wikipedia: Joule; Wikipedia: James Prescott Joule
Horsepower-hour (hp⋅h)
About 2.685 MJ (0.7457 kWh), the energy of one mechanical horsepower for an hour.
Multiplying a power by a time gives energy, and this unit does it with James Watt's horse. In the late 18th century Watt compared steam engines with the draft horses they replaced. After an experiment in 1782 that suggested a brewery horse delivered 32,400 foot-pounds per minute, he and Matthew Boulton rounded the figure to 33,000 foot-pounds per minute the next year. One mechanical horsepower is therefore about 745.7 W, and sustaining it for an hour gives roughly 2.685 MJ, or 0.7457 kWh.
The unit is now outdated and outside the SI. Railways still use it to settle accounts when locomotives are lent between companies. In one example, a 2,500 hp unit used for 12 hours is owed back as 30,000 hp-hours, repayable with a 3,000 hp unit for 10. A German variant, the Pferdestaerkenstunde, uses the metric horsepower of about 735.5 W and equals 2,647.7955 kJ, so one hp-hour is about 1.014 PSh.
1 horsepower-hour = 2,684,519.538 joules (approximately).
Sources: Wikipedia: Horsepower-hour; Wikipedia: Horsepower; Wikipedia: Conversion of units of energy
Related conversions
- Horsepower-hours to joules (reverse)
- Joules to kilojoules
- Joules to watt-hours
- Joules to kilowatt-hours
- Joules to British thermal units
- Joules to calories
- Joules to kilocalories
- Joules to megajoules
- Joules to gigajoules
- Joules to megawatt-hours
- Joules to foot-pounds
- Joules to millijoules
- Joules to electronvolts
- Kilojoules to horsepower-hours
- Watt-hours to horsepower-hours
- Kilowatt-hours to horsepower-hours
- British thermal units to horsepower-hours
- Calories to horsepower-hours
- Kilocalories to horsepower-hours
See all energy units.