How do you convert Horsepower (Electric) to Watt?

Multiply the value in Horsepower (Electric) (hp) by the conversion factor to get the result in Watt (W).

Convert Horsepower (Electric) to Watt (hp to W)

Reference ID: EC-POWE-HPW | EngConverter Calculation Guide

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In engineering, power conversion between different units is essential for design and analysis. The horsepower (electric) and the watt (W) are two common units of power used in electrical and mechanical systems. Understanding their relationship allows engineers to seamlessly translate ratings across different applications.

Horsepower (Electric)

Horsepower is a unit of power originally defined by James Watt to compare steam engine output to draft horses. The electric horsepower is a specific variant used primarily for electric motors and generators. By definition, one electric horsepower equals exactly 746 watts. It is commonly found on nameplates of electric motors, pumps, and compressors. When engineers specify motor ratings in horsepower, they implicitly reference the mechanical output power at the shaft.

Watt (W)

The watt is the SI derived unit of power, named after James Watt. It measures the rate of energy transfer or conversion. One watt equals one joule per second. In electrical systems, watts represent instantaneous power consumption or generation. Practical applications include sizing power supplies, calculating heat loads, and specifying lighting or heating elements. The watt is universally used in science and engineering because it integrates seamlessly with other SI units such as volts and amperes.

Conversion Principle

The conversion between electric horsepower and watts is straightforward: \$ 1\,hp = 746\,W \$. To convert from horsepower to watts, multiply the horsepower value by 746. Conversely, divide watts by 746 to obtain electric horsepower. This linear relationship simplifies power budgeting in combined electrical and mechanical systems.

Practical Applications

Electric motors: A 5 hp motor corresponds to \$ 5 \\times 746 = 3730\,W \$. Engineers use this to match wiring and thermal management.
Generators: Output is often stated in kW or hp. Converting ensures the prime mover (e.g., diesel engine) meets electrical load requirements.
HVAC systems: Fan and compressor motors are rated in hp; cooling capacity is in watts or BTUs. Conversion aids in system balancing.
Renewable energy: Wind turbine or hydro turbine ratings may be given in hp; converting to watts helps compare to solar arrays or grid tie-in specifications.

Horsepower (Electric) to Watt Conversion Reference Table

Horsepower (Electric) (hp)	Watt (W)
0.1	74.6
0.5	373
1.0	746
2.0	1492
5.0	3730
10.0	7460
20.0	14920
50.0	37300
100.0	74600
500.0	373000
1000.0	746000

Example: Convert 10 Horsepower (Electric) to Watts

Follow these three steps to perform the conversion.

Write the conversion formula: \$\$ P(W) = P(hp) \\times 746.0 \$\$
Substitute the given value: \$\$ P(W) = 10 \\times 746.0 \$\$
Calculate the result: \$\$ P(W) = 7460\,W \$\$

Therefore, 10 electric horsepower is equivalent to 7460 watts.

The electric horsepower is defined as exactly 746 watts, whereas mechanical horsepower is approximately 745.7 watts (or 33,000 ft·lb/min). The difference is about 0.3 watts (0.04%). While negligible in many applications, engineers must use the correct definition when precise power ratings are required, especially in large motor systems or when calculating energy costs over time.

The value of 746 watts per horsepower was standardized by international agreement. It comes from the original definition of horsepower (550 ft·lb/s) converted to SI units using the meter (0.3048 m per foot) and the kilogram-force (9.80665 N per pound-force) resulting in approximately 745.7 W. For electrical applications, the round number 746 W was adopted to simplify calculations and calibration of electric motor testing equipment.

"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison."
"Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house."
— Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)