Horsepower is a unit of mechanical power, while kVA (kilo-Volt-Amperes) is a unit used for rating the output of electrical devices. In electrical terms, 1 horsepower equals 746 Watts, but converting kVA to horsepower requires also knowing the Power Factor of the electrical device (how efficiently the electrical device uses electricity). An Industry-Standard average rating of 60 percent (for motors) or 80 percent (for other electrical devices) can be used if the actual Power Factor is not known. Using this Power Factor along with the known kVA numbers will give an approximate yet still reliable understanding of the kVA’s horsepower equivalent.
Determine the Power Factor of the device you are referring to. If you do not have the Power Factor in the device’s documentation, use 0.6 for a motor (60-percent rating) or 0.8 for any other type of electrical device (80-percent rating).
Multiply the kVA rating by the Power Factor to determine the kilowatts. If the kVA rating was 20, for example, and the Power Factor was 60 percent, the equation would read 20 x 0.6 = 12 kW.
Change the kW answer to Watts by multiplying it by 1,000 (‘kilo’ is a prefix meaning ‘thousand,' so a kilowatt means a thousand Watts). In our example, 12 kW x 1,000 = 12,000 Watts.
Convert the Watts to horsepower through dividing Watts by 746 (because 1 horsepower equals 746 Watts). In our example, 12,000 / 746 = 16.085, or about 16 horsepower. In summary, (kVA x PF x 1,000) / 746 = horsepower.
Tips
The electrical device’s Power Factor can range from 40% to 95% and, unfortunately, is never printed on the equipment nameplate. The exact Power Factor of an electrical device can occasionally be found in the device’s manufacturing specs, if those specs are available.
Warnings
If you are trying to determine how powerful an electrical device you need for a specific application, be sure to check with a professional electrical engineer to ensure your requirements are met adequately.
