Horsepower (hp) measures the amount of mechanical energy a device uses to complete a task. An air compressor converts electrical energy into mechanical energy to move air or liquid particles. Typically electrical power is measured in watts which equals a single joule of energy consumed every second. A single unit of horsepower is equivalent to 745.8 watts. A watt meter allows you to calculate the horsepower of a compressor by first finding its power in watts.

Turn on the watt meter.

Plug the compressor into the watt meter. Note the number of watts of power the device draws. For example, the power might be 1500.0 watts.

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Convert the power to horsepower by dividing by 745.8. In our sample exercise, 1500.0 watts divided by 745.8 watts equals 2.0 horsepower.