CFM

CFM stands for cubic feet per minute and measures the volume of air a compressor can deliver, usually rated at a specific pressure like 90 PSI. It is the number that determines whether a compressor can keep up with a tool's actual air demand or whether the tool will stall as the tank drains faster than the pump can refill it.

Tools vary enormously in how much air they need. A basic brad nailer or a tire inflator sips air and can run off a small compressor with a modest CFM rating, while an impact wrench, a sander, or spray equipment used continuously needs a much higher sustained CFM, not just a big tank. A large tank with a small pump can run a demanding tool briefly, then leave you waiting for pressure to rebuild.

When comparing compressors, it helps to check the CFM rating at the pressure your tools actually use rather than just the peak number on the box, since CFM drops as required pressure rises. A common mistake is buying based on tank size alone and being surprised when a continuous-use tool bogs down the compressor within a minute of steady work.