Once you've identified the type of nozzle you need, before you go any further, you need to understand  a little bit more about your air compressor. If we had a pound for everytime someone told us that they had a 'big' air compressor, we'd retire early.

Unfortunately, the physical size of the compressor may not bear any realtionship to the size of nozzle it can 'drive'. When we say 'size', we mean the hole or bore size of the nozzle of course...The action bit, where all the grit and air passes through...

It's all about CFM Vs Blasting Pressure. You're compressor will have a CFM rating; how much free air it can deliver. 

There is a quick rule-of-thumb, you can use as a guide to determine your CFM (Free AIr Delivery Cubic Feet Per Minute)

For a piston compressor multiply the horse power by 3 and by 4 for a vane compressor..

More information on CFM etc., the bottom of the page...