A general rule of thumb for blast nozzle sizing is to use an air compressor that is 50% larger than needed for your nozzle.
New blast nozzles wear rapidly and require more CFM the more they wear. At 100 psi a new 1/4" sandblast nozzle only needs
an 18 hp compressor. After some time that 1/4" nozzle will wear to 5/16" then to 3/8" and larger. The nozzle will now flow more
and requires a larger compressor. Looking at the chart 5/16" requires 30.5 hp at 100psi. 3/8" requires 44 hp at 100 psi. If you
have a 30 hp compressor you can use a 1/4" nozzle until it wears to 5/16" then it must be replaced. If you have a 44hp compressor
you can use a 1/4" nozzle until it wears to 3/8". Nozzles are expensive. The 44 hp compressor would require fewer nozzle changes
than a 30 hp compressor in this example.