Electrical Horsepower to Watts (hp (E) to W)

1 electrical horsepower equals 746 watts exactly.

How to convert electrical horsepower to watts

To convert electrical horsepower to watts, multiply the number of electrical horsepower by 746. This factor is exact. To go the other way, multiply watts by 0.001340482574 (rounded).

watts = electrical horsepower × 746

Example: 10 electrical horsepower = 7,460 watts.

Several different horsepower units exist. This site lists mechanical (745.7 W), metric (735.5 W) and electrical (746 W) horsepower separately.

About these units

Electrical Horsepower (hp (E))

US & ImperialCurrent unit

Exactly 746 watts, the horsepower used for electrical power.

Electrical horsepower exists because electric motors needed a rating that fits neatly with watts. Mechanical horsepower goes back to James Watt, who compared steam engines with brewery horses and, with Matthew Boulton, settled on 33,000 foot-pounds per minute in 1783. That works out to about 745.7 watts. The electrical version rounds the figure to exactly 746 watts, so that motor ratings convert cleanly to kilowatts.

The difference from the mechanical unit is under 0.05 percent, far smaller than the gap to the metric horsepower of about 735.5 watts, which is roughly 98.6 percent of the imperial one. A motor nameplate normally states shaft output, not the electrical power drawn from the supply, and US nameplates use horsepower where most other countries use watts or kilowatts. NIST lists the electric horsepower as exactly 746 watts.

1 electrical horsepower = 746 watts (exactly).

Sources: Wikipedia: Horsepower; NIST SP 811, Appendix B.8

Watt (W)

Metric (SI)Current unit

The SI unit of power: one joule per second. A typical LED bulb uses 5–10 W and a laptop 30–60 W.

Credit for the name goes to C. William Siemens, who proposed it in August 1882 in his presidential address to the British Association for the Advancement of Science. He chose it to honor James Watt, the Scottish inventor who in 1776 improved the Newcomen steam engine. An International Conference on Electric Units and Standards adopted Siemens' definition in London in October 1908 as the international watt. After the 1948 General Conference on Weights and Measures the unit was redefined in absolute terms, and in 1960 the 11th General Conference adopted it into the SI as the unit of power.

Today one watt is one joule per second, or equivalently one volt times one ampere. Orders-of-magnitude tables put an LED light bulb at about 7 W and an adult's basal metabolic rate at roughly 100 W. A 100 kg person climbing a 3 m ladder in 5 seconds works at about 600 W, while a laborer can sustain around 75 W over an eight-hour day. The watt measures a rate, so it says how fast energy is being used, not how much has been used in total.

The watt is the reference unit for power on this site.

Sources: Wikipedia: Watt; Wikipedia: Orders of magnitude (power)

Related conversions

See all power units.