Power Converter

Convert Watts, Horsepower (hp), and BTUs

Last updated: 10/8/2026

Data sources:NIST Special Publication 811, Appendix B: Conversion factors

Enter a power in watts, kilowatts, mechanical or electrical horsepower, or BTU per hour and the converter lists the same power in all five units. Engines are rated in horsepower, motors and generators in kilowatts, and heating and cooling equipment in BTU/hr, so the same quantity of power is routinely quoted three different ways.

Calculator Inputs

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The converter changes units only. It does not convert between input and output power or apply motor, engine, or heat-pump efficiencies.

How It Works

Power is energy per unit time. The value is first converted to watts: 1 kW = 1,000 W; 1 mechanical hp = 550 ft·lbf/s = 745.699872 W; 1 electrical hp = 746 W by definition; 1 BTU/hr = 1,055.056 J ÷ 3,600 s = 0.293071 W. Reversed: 1 kW = 1.34102 hp = 3,412.14 BTU/hr.

Which horsepower?

Mechanical (imperial) horsepower, 745.7 W, is the unit used for car and small-engine ratings in the US and UK. Electrical horsepower is rounded to exactly 746 W and is used on motor nameplates. Metric horsepower (PS, CV, ch), 735.5 W, is used for European car ratings and is not offered here; multiply PS by 0.9863 to get mechanical hp. The three differ by about 1.4%, which matters when comparing published engine figures.

BTU/hr and tons of cooling

Air conditioners are often rated in tons: 1 ton of cooling is 12,000 BTU/hr, or about 3.517 kW of heat removed. A 2-ton unit therefore moves 24,000 BTU/hr (7.03 kW) of heat. That is the heat it removes, not the electrical power it draws, which is lower by the unit's efficiency ratio.

Worked example

A 5 hp (mechanical) compressor motor in kilowatts and BTU/hr

Watts:5 hp × 745.699872 W/hp= 3,728.50 W

Kilowatts:3,728.50 W ÷ 1,000= 3.7285 kW

Electrical hp:3,728.50 W ÷ 746 W/hp= 4.998 hp

BTU per hour:3,728.50 W × 3.412142 BTU/hr per W= 12,722.2 BTU/hr

Tips & Best Practices

•Mechanical horsepower is standard for engine ratings; electrical horsepower (746 W) appears on motor nameplates.
•A motor's nameplate hp is output power. Electrical input is higher by the motor's efficiency, typically 1.1 to 1.25 times the output for small motors.
•To convert a kW rating to BTU/hr, multiply by 3,412; to go the other way, divide by 3,412.

Frequently Asked Questions

How many watts are in one horsepower?

745.7 W for mechanical horsepower (exactly 745.699872 W), 746 W for electrical horsepower, and 735.5 W for metric horsepower (PS). The converter offers the first two.

Why is 1 kW equal to 3,412 BTU/hr?

One BTU (International Table) is 1,055.056 J. One kilowatt delivers 1,000 J every second, which is 3,600,000 J per hour; divided by 1,055.056 J gives 3,412.14 BTU/hr.