In air compressors, the abbreviation "CFM" stands for cubic feet per minute, a measurement of the flow rate of a volume of air. When using an pneumatic-powered tool connected to an air compressor, each tool has a minimum "CFM" rating for optimal operation.
When attaching multiple pneumatic tools to a single compressor, the "CFM" rating of each tool is added together. If using three tools that need five cubic feet per minute of air pressure, for example, a single air compressor must be able to provide at least 15 cubic feet per minute of air. Generally, continuously used pneumatic tools like grinders and sanders have significantly higher "CFM" requirements than intermittent-operation tools like drills and or impact wrenches.