Horsepower-hours to Watt-hours (hp⋅h to Wh)
1 horsepower-hour equals 745.6998716 watt-hours (rounded).
How to convert horsepower-hours to watt-hours
To convert horsepower-hours to watt-hours, multiply the number of horsepower-hours by 745.6998716. The factor is rounded to 10 significant digits. To go the other way, multiply watt-hours by 0.00134102209 (rounded).
watt-hours = horsepower-hours × 745.6998716
Example: 10 horsepower-hours = 7,456.998716 watt-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
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The unit is now outdated and outside the SI.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
Watt-hour (Wh)
Exactly 3,600 joules, the energy used by a one-watt device in an hour. Battery capacities are quoted in watt-hours.
Pair a power unit with a unit of time and you get the watt-hour: one watt sustained for one hour, which works out to 3,600 joules. The watt itself was adopted at the second International Electrical Congress in 1889, in the same session that adopted the joule, so the two units share a birthday even though the watt-hour is the one people read off batteries.
Battery capacity is where it earns its keep. Multiplying amp-hours by the battery voltage gives an estimate of watt-hours, so a 2,500 mAh lithium-ion cell at 3.7 V holds roughly 9.25 Wh. That is why a 500 mA USB device runs about 3.7 hours on it rather than five: the cell voltage, not the 5 V from the port, sets the energy.
For scale, an alkaline AA battery holds about 9 kJ, which is 2.5 Wh. A 12 W LED lamp left on for an hour uses 12 Wh, and a 40 W appliance running for 25 hours uses 1,000 Wh.
1 watt-hour = 3,600 joules (exactly).
Sources: Wikipedia: Watt-hour; Wikipedia: Joule; Wikipedia: Orders of magnitude (energy)
Related conversions
- Watt-hours to horsepower-hours (reverse)
- Horsepower-hours to joules
- Horsepower-hours to kilojoules
- Horsepower-hours to kilowatt-hours
- Horsepower-hours to British thermal units
- Horsepower-hours to calories
- Horsepower-hours to kilocalories
- Joules to watt-hours
- Kilojoules to watt-hours
- Kilowatt-hours to watt-hours
- British thermal units to watt-hours
- Calories to watt-hours
- Kilocalories to watt-hours
- Megajoules to watt-hours
- Gigajoules to watt-hours
- Megawatt-hours to watt-hours
- Foot-pounds to watt-hours
- Millijoules to watt-hours
- Electronvolts to watt-hours
See all energy units.