When it comes to abrasive blasting the more air you have the better. While the amount of air needed depends on the a variety of factors including the nozzle size and blasting pressure. How do really know how much air your compressor is generating.
Compressors will often have a data plate that identifies the air volume (cfm) generated at a specific pressure (psi). This information is a good step towards identifying how much will be available at the actual blasting pressure. The actual cfm generated is generally less than the stated amount even when factoring in changes in psi.
A good rule of thumb is that the each horsepower will generate 4 cfm of air at 100 psi. To get these results, the tank size should be at least 1 gallon for each cfm generated by the compressor.