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Fractional horsepower motors typically have a frame smaller than that of a motor with a continuous rating of one horsepower at 1800 rpm. It is the frame size, rather than the motor rating, that defines a fractional horsepower motor, and some units can actually have ratings above one horsepower. Frame sizes are specified by National Electrical Manufacturers Association (NEMA) standards, and motors up to a frame size of 56 can be classified as fractional horsepower.

Uses for these devices include heating and cooling equipment, pumps and certain low-grade water propulsion applications. Fractional horsepower motors also drive a variety of ventilators, industrial blowers and exhaust fans. Additionally, certain small medical devices use fractional horsepower motors, as do select computer and office machine components. Even telecommunication and exercise equipment incorporate fractional horsepower motors into their design.

Most fractional horsepower motors are electric, and share characteristics common to all electric motors. Like their larger counterparts, they utilize electromagnets and a rotating shaft to convert AC (alternating current) or DC (direct current) electricity to mechanical energy. In a typical electric motor, electricity is sent through the coils wrapped around the rotor, thereby supplying the rotor with a magnetic field. This field forces the rotor to turn in order to align its poles with the stationary magnets around it. Before the poles align, contacts inside the motor known as brushes change the nature of the field, causing the rotor to continue its rotation (brushless motors accomplish this through a more complex method). The motion of the rotor drives the shaft and translates electricity into mechanical energy.

Fractional horsepower motors generally weigh less than a few ounces and tend to be only a few inches in length, or smaller. They are often manufactured by companies that also produce larger motors, who account for a large portion of the total FHP sales.