*This article may have affiliate links, which means we may receive commissions if you choose to purchase through links we provide (at no extra cost to you). For more details, please read our privacy policy/affiliate disclosure. Thank you for supporting the work we put into this blog!

Horse­pow­er (hp) is a unit of mea­sure­ment of pow­er (the rate at which work is done). There are many dif­fer­ent stan­dards and types of horse­pow­er. The most com­mon horsepower—especially for elec­tri­cal power—is 1 hp = 746 watts. The term was adopt­ed in the late 18th cen­tu­ry by Scot­tish engi­neer James Watt to com­pare the out­put of steam engines with the pow­er of draft hors­es. It was lat­er expand­ed to include the out­put pow­er of oth­er types of pis­ton engines, as well as tur­bines, elec­tric motors and oth­er machin­ery. The def­i­n­i­tion of the unit var­ied between geo­graph­i­cal regions. Most coun­tries now use the SI unit watt for mea­sure­ment of pow­er. With the imple­men­ta­tion of the EU Direc­tive 80/181/EEC on Jan­u­ary 1, 2010, the use of horse­pow­er in the EU is per­mit­ted only as a sup­ple­men­tary unit.