This depends on some personal factors. The most important of these are the dimensions of the area and the magnitude of the job. For most people, a CFM between 150 to 200 is adequate.  Most homeowners only need to clean up their lawns, backyards, driveways, and verandas. If you have a larger property or a problem with wet debris, a leaf blower with a CFM between 400 to 700 is better suited. For more professional work in a commercial setting such as a parking lot, you would need an even higher CFM. CFMs can go as high as 3000 for heavy and louder models.