Rated on cubic feet per minute of air volume output (cfm), pounds per square inch of air pressure input (psi) and horsepower (hp). The higher the ratings on any of these, the more versatile the compressor.
The most important rating is the cfm, because it indicates the amount of air volume needed to operate various tools. Match the cfm rating on the compressor to the cfm rating on the tool when buying a compressor.
Compact or portable compressors use a diaphragm-type compression pump powered by an electric motor. They are best used for light applications such as inflation or light spray painting.
Piston-type compressors use an electric or gasoline motor to drive the pump unit. They offer durability and high work capacity.