To establish the air space inside the “box” (i.e. your cabinet/dust collector) you take the height, width, and length measurements and multiply them to arrive at the air volume number, which is in cubic inches. To get the cubic feet, you have to divide that number by 1,728 (which is equal to 1 cubic foot).
If you are using separate components, you need to check on the capacity of the vacuum system you plan to use with your cabinet. The capacity has to do with the motor of the vacuum system and how large the filter system is. You want to have a dust collector that can exchange the air space inside your cabinet at the minimum 10 times per minute; of course, more is better … to a point. You don’t want a vacuum that is so strong that you can’t move your hands and that would suck out all your abrasive while blasting.
-Ruth Dobbins, EtchMaser