Horsepower-hours to Kilojoules (hp⋅h to kJ)

1 horsepower-hour equals 2,684.519538 kilojoules (rounded).

1 horsepower-hour = 2,684.519538 kilojoules

How to convert horsepower-hours to kilojoules

To convert horsepower-hours to kilojoules, multiply the number of horsepower-hours by 2,684.519538. The factor is rounded to 10 significant digits. To go the other way, multiply kilojoules by 0.000372506136 (rounded).

kilojoules = horsepower-hours × 2,684.519538

Example: 10 horsepower-hours = 26,845.19538 kilojoules.

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)

US & ImperialTraditional unit (still used in some regions)

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The unit is now outdated and outside the SI.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

Kilojoule (kJ)

Metric (SI)Current unit

1,000 joules. Food labels in many countries give energy in kilojoules.

Most food labels around the world express energy in kilojoules, which is the calorie's long retirement in action. The calorie came out of heat measurement, and the 1948 CGPM resolution stated that the joule should be preferred as the unit of heat. Labels that still show kilocalories alongside kilojoules rely on the thermochemical calorie of exactly 4.184 joules, so one kilocalorie is about 4.184 kJ.

The kilojoule is a convenient size for a body's daily bookkeeping. A person at rest uses about 5,000 kJ, or roughly 1,200 kcal, per day, and the recommended intake for a moderately active woman is given as 2,000 food calories, which is about 8,400 kJ.

Smaller physical comparisons land in the same range. One watt-hour is 3.6 kJ, a British thermal unit is about 1.1 kJ, exploding a gram of TNT releases about 4.2 kJ, and an alkaline AA battery holds about 9 kJ.

1 kilojoule = 1,000 joules (exactly).

Sources: Wikipedia: Kilojoule; Wikipedia: Joule; Wikipedia: Orders of magnitude (energy)

Related conversions

See all energy units.