Pressure is not normally the issue as most compressors go up to about 100 psi and most guns need only 35~50 psi at the inlet.   Its more about the volume needed from the compressor/tank system to keep up with what your gun requires.  For a full size gun I would suggest at least a 20 gallon tank.  Detail guns would work OK with the smaller pancake type units used for pneumatic nail guns.  
What gun do you have or looking at getting ?  Check the manufactures specs on the gun for the CFM required and try to match that to the compressor's output.  You can get by with a lower compressor CFM rating than the gun CFM with a larger tank volume.