To answer this question, we have to leave until the end of the eighteenth century. England was positioned as the first world power motivated by the advances that took place during the First Industrial Revolution, being the main protagonist of the same the Scottish James Watt. Inventor of the improved steam engine (from the work previously done by Thomas Newcomen), was also the first to coined the term horsepower (HP).
It is estimated that this took place around 1782, and that its purpose was none other than to create a non-absolute measure between the power of its steam engines and that of draft horses. That is, with horses used in some cases as a driving force when moving the mechanism of certain machines. The reason for this comparison is that Watt wanted to convince the public that the use of the steam engine was much more powerful and effective than the obsolete traditional use of horses. In this way, he established that a horse had the strength to lift by itself a weight of 330 pounds at a height of 100 feet, in our metric system a weight of 149.68kg at a height of 30.48 meters per minute. By modifying the height, according to Watt, a horse would be able to lift 75kg at one meter per second. Visually, in relation to weight and height, imagine a horse that moves a pulley that contains a bucket full of coal. Well, Watt promised that with the steam engine, loads of 150 kg could be lifted at a speed of 1.82 km / hour (doing metric conversions).
It should be noted that this measure is not absolute at all, but an estimate of Watt in relation to the strength of a medium horse, with which to establish such a comparison. We could therefore affirm that this concept was in itself, a great marketing campaign. Currently, the use of horsepower (Horsepower), continue to have considerable relevance in the Anglo-Saxon countries. The mistake of converting HP into CV often arises. That is, to confuse the horsepower with steam.
To give an example, if we take the Range Rover of 2018, it has a 3.0-liter, 258 HP TDV6 engine option. If we measured the horses in horsepower, the figure would be reduced to 254 HP, but the mechanical power in both cases would be the same. Why? Steam horses (HP) were established as a unit of measure equivalent to horsepower for the creation of the French metric system. Being its original term cheval-vapeur, the difference in absolute terms is only 1.37% greater CV than HP, all a convoluted conversions to measure the power, which culminated with the creation of Watt (Watt in English in honor of Watt) as the unit of the International System of Units for power. Therefore if the Range Rover, equips a 254 HP engine, we could also say that it equips an engine of 189.408 W (1 HP = 745.7 W).