hp to Watts Converter

How to convert hp to watts?

Converting horsepower to watts links the traditional mechanical power unit with the SI watt, essential for electrical engineering, motor sizing, generator specification, and translating older industrial equipment to modern metric standards. One mechanical horsepower (the US/UK standard) equals exactly 745.7 watts, so multiplying hp by 745.7 yields watts. For metric horsepower (PS) the factor is 735.5. Our converter uses mechanical horsepower, the dominant standard in English-speaking countries. Examples: 1 hp is 745.7 W, 10 hp is 7,457 W, and 100 hp is 74,570 W. Useful for sizing wires, breakers, transformers, and inverters.

P_(W) = P_(hp) × 745.7

Example

Convert 1 hp to watts:

P_(W) = 1 hp × 745.7 = 745.7 W

How many watts in a horsepower?

One mechanical horsepower equals exactly 745.7 watts, the US/UK convention. One metric horsepower (PS) equals 735.5 watts, the European convention. Most spec sheets in the English-speaking world use mechanical hp, while German, French, and Italian car catalogs use PS. For most engineering work, either value is close enough to the standard 750 W approximation. The exact 745.7 W comes from defining mechanical horsepower as 550 foot-pounds per second of work, which translates to 745.69987 watts to seven significant figures.

How many horsepower in a watt?

One watt equals approximately 0.001341 mechanical horsepower, the reciprocal of 745.7. Equivalently, 1,341 watts is just under 2 hp. For mental shortcuts, 1 kilowatt is roughly 1.34 hp, 5 kW is about 6.7 hp, and 10 kW is about 13.4 hp. Working backwards, a 1-hp electric motor draws roughly 750 watts at full load. Adjust for efficiency: a real motor might pull 850 to 900 watts from the wall to deliver 1 hp of mechanical output, depending on its efficiency rating.

What is the conversion formula?

The formula is watts = hp multiplied by 745.7. So 10 hp times 745.7 equals 7,457 W, and 100 hp equals 74,570 W. To go the other way, divide watts by 745.7 to get hp. The factor 745.7 reflects the mechanical horsepower definition by James Watt in the late 18th century, when he calibrated his steam engines against the work rate of a typical draft horse lifting 550 pounds one foot per second. The exact value to seven significant figures is 745.69987 watts per mechanical horsepower.

Why convert hp to watts for electrical work?

Electrical calculations use watts (and kilowatts) for sizing wires, breakers, transformers, and inverters. Motor nameplates often quote both horsepower (mechanical output) and watts (electrical input), but older equipment may show only hp. To size a circuit for a 5-hp motor, multiply 5 by 745.7 to get 3,729 watts of mechanical output, then divide by motor efficiency (typically 0.85 to 0.95) to estimate electrical input around 4,200 watts. From there, divide by line voltage to get amps for breaker sizing.

Are mechanical and electrical horsepower the same?

There's no separate 'electrical' horsepower in the strict sense, but some older US conventions used 746 W as an 'electrical horsepower' definition for rating motors. Today most standards have consolidated around mechanical horsepower at 745.7 W. The very small difference (less than 0.05 percent) rarely matters in practice. Always check the standard your country uses: NEMA in North America, IEC internationally, and JIS in Japan. They all converge on the same hp value within a fraction of a percent.

How is hp used in marine engines?

Boat motor ratings range from a few hp for trolling motors (often quoted as 'thrust pounds' instead) to thousands of hp for large yacht diesels. A typical recreational outboard might be 25 to 250 hp, which translates to 18.6 to 186 kW. Marine engineers convert to watts when calculating fuel burn rates, alternator capacity, and electrical load budgets on board. The conversion also matters when matching propeller pitch to engine power, since pitch tables in metric countries reference engine kW rather than hp.

What is the watt?

The watt is the SI unit of power, defined as one joule of energy per second. It was named after James Watt for his improvements to the steam engine. One watt represents a small amount of power: a typical LED light bulb uses about 8 to 15 watts, a smartphone charges at 5 to 20 W, and a human at rest produces about 80 to 100 W of body heat. Kilowatts (1,000 W) measure household appliances, megawatts (million W) measure power plants, and gigawatts (billion W) measure grid-scale infrastructure.

Popular hp to watts conversion table