SoupCalc

Power Converter — Watts, Kilowatts, Horsepower, and Btu per Hour

Power Converter

Power is the rate at which energy is transferred or work is done. This converter uses the watt as its internal reference and supports W, kW, MW, GW, mW, mechanical horsepower, International Table Btu per hour, and joules per second.

Enter a finite numeric value, choose the source unit, and choose the target unit. The calculator multiplies the input by the source unit’s watt factor and divides by the target unit’s watt factor. Negative values are mathematically valid when a sign convention represents power flowing in the opposite direction.

Unit definitions

The SI relationship is 1 W = 1 J/s. Decimal prefixes are exact, so 1 kW = 1,000 W, 1 MW = 1,000,000 W, 1 GW = 1,000,000,000 W, and 1 mW = 0.001 W.

For the non-SI units implemented here:

  • 1 hp = 745.699872 W for mechanical horsepower based on 550 foot-pound-force per second;
  • 1 Btu/h = 0.293071070 W using the International Table Btu;
  • 1 J/s equals 1 W by definition.

The label “horsepower” is not universal. Metric horsepower, electrical horsepower, boiler horsepower, and tax horsepower have different meanings and are not options on this page.

Worked example

Convert 5 mechanical horsepower to kilowatts:

5 hp × 745.6998715822702 W/hp = 3,728.4993579 W

3,728.4993579 W ÷ 1,000 = 3.7284993579 kW

The displayed result may be rounded for readability, while the calculation retains the stored factor.

What the result means

Equivalent power values describe the same rate in different units. A 1 kW device transfers 1,000 joules of energy each second while operating at that power. Conversion does not predict efficiency, energy consumption, heat loss, electrical current, torque, or equipment capacity.

Most importantly, power is not energy. Kilowatts measure a rate; kilowatt-hours measure accumulated energy. A 1 kW load running for three hours consumes 3 kWh, not 3 kW.

Accuracy and limitations

The result is only a unit conversion. Equipment nameplates may distinguish input, output, shaft, brake, thermal, apparent, real, peak, or continuous power. Those quantities cannot be interchanged merely because they share a power unit.

Confirm which horsepower and Btu definitions a source uses. The converter uses mechanical horsepower and the International Table Btu per hour. It does not model power factor, duty cycle, efficiency, temperature derating, startup load, or measurement uncertainty. Use manufacturer data and a qualified engineer for equipment selection or electrical safety decisions.

Sources

Editorial record

Written and conversion-checked by the SoupCalc Editorial Team. Watt, prefix, horsepower, Btu/h, and joule-per-second cases are covered by automated tests against the stored unit factors.

Last reviewed: August 10, 2026.