CFM (cubic feet per minute) lets you know how fast the air compressor will work. For powerful tools, you need an air compressor with large tank. However, higher CFM will ensure the pressure stays longer. As gases can change the pressure based on humidity, temperature and other factors, CFM can be a variable option. Some brands list CFM in a way that doesn’t correspond to real-world conditions. This actually makes the whole air compressor look heavier that it is. SCFM reads for standard cubic feet per minute. It is actually calculated CFM based on extraneous factors held constant. This lets you compare the models properly.